Просмотр кода страницы Английская Википедия:Imperial and US customary measurement systems

{{Английская Википедия/Панель перехода}}
{{Short description|English (pre 1824), Imperial (post 1824) and US Customary (post 1776) units of measure}}
{{Use dmy dates|date=December 2020}}
[[File:CincinnatiCustomsHouse.jpg|thumb|upright=1.35|[[United States Custom House and Post Office (Cincinnati)|Cincinnati Customs House]] {{circa}} 1850–60<br>Governments were one of the earliest users of weights and measures – often for the purpose of tax collection.  In the United States the [[United States Department of the Treasury|US Treasury]] rather than [[United States Congress|Congress]] took the lead in establishing a standard [[system of weights and measures]].]]
The '''imperial and US customary measurement systems''' are both derived from an earlier [[English units|English system of measurement]] which in turn can be traced back to [[Ancient Roman units of measurement]], and [[Carolingian Renaissance|Carolingian]] and [[Saxons|Saxon]] units of measure.

The [[United States customary units|US Customary system of units]] was developed and used in the United States after the [[American Revolution]], based on a subset of the English units used in the [[Thirteen Colonies]]; it is the predominant system of units in the United States and in [[Territories of the United States|U.S. territories]] (except [[Puerto Rico]] and [[Guam]], where the [[metric system]] is also officially used and is predominant, which was introduced when both territories were [[Spanish America|Spanish colonies]]).<ref>{{Cite web|last=|first=|title=US leaves the world puzzled by dragging its feet on metric system|url=https://www.nationthailand.com/perspective/30275741|date=2015-12-26|access-date=2023-01-28|website=The Nation Thailand}}</ref> The [[Imperial units|imperial system of units]] was developed and used in the United Kingdom and [[British Empire|its empire]] beginning in 1826. The [[metric system]] has, to varying degrees, replaced the imperial system in the countries that once used it.

Most of the units of measure have been adapted in one way or another since the [[Norman Conquest]] (1066). The units of linear measure have changed the least – the [[yard]] (which replaced the [[ell]]) and the [[chain (unit)|chain]] were measures derived in England. The [[foot (unit)|foot]] used by craftsmen supplanted the longer foot used in agriculture.  The agricultural foot was reduced to {{fract|10|11}} of its former size, causing the [[Rod (unit)|rod, pole or perch]] to become {{fract|16|1|2}} (rather than the older 15) agricultural feet.  The [[furlong]] and the [[acre]], once it became a measure of the size of a piece of land rather than its value, remained relatively unchanged. In the last thousand years, three principal pounds were used in England. The [[troy pound]] (5760 [[grain (unit)|grains]]) was used for precious metals, the [[Apothecaries' system|apothecaries' pound]], (also 5760 grains) was used by [[pharmacist]]s and the [[avoirdupois pound]] (7000 grains) was used for general purposes. The apothecaries and troy pounds are divided into 12 ounces (of 480 grains) while the avoirdupois pound has 16 ounces (of 437.5 grains). The unit of volume, the [[gallon]], has different values in the United States and in the United Kingdom – the US fluid gallon being about 0.83 imperial gallons and the US dry gallon being about 0.97 imperial gallons. The US fluid gallon was based on the wine gallon used in England prior to 1826.

After the [[United States Declaration of Independence]] the units of measurement in the [[United States]] developed into what is now known as [[United States customary units|customary units]]. The United Kingdom overhauled its system of measurement in 1826, when it introduced the [[imperial units|imperial system of units]]. This resulted in the two countries having different gallons. Later in the century, efforts were made to align the definition of the [[pound (avoirdupois)|pound]] and the [[yard]] in the two countries by using copies of the standards adopted by the British Parliament in 1855. However, these standards were of poor quality compared with those produced for the [[Convention of the Metre]]. In 1960 the two countries agreed to common definitions of the yard and the pound based on definitions of the [[metre]] and the [[kilogram]]. This change, which amounted to a few parts per million, had little effect in the United Kingdom, but resulted in the United States having two slightly different systems of linear measure – the international system, and the surveyors system.

== English units of measure==
{{main|English units}}
[[File:Aethelstan.jpg|thumb|upright|Silver penny of [[Æthelstan]] (924-939) from which the name ''[[pennyweight]]'' (dwt) was derived]]

English units of measure, were derived from a combination of [[Ancient Roman units of measurement|Roman]], [[Carolingian Renaissance|Carolingian]] and [[Saxons|Saxon]] units of measure.  They were a precursor to both the [[Imperial units|imperial system of units]] (first defined in 1824, to take effect in 1826) and [[United States customary units]] which evolved from English Units from 1776 onwards.<ref name=Smoot/>

The earliest records of English units of measure involve the weight (and therefore the value) of [[Saxons|Saxon]] coins.  The [[penny]] introduced by [[Offa of Mercia|Offa]] was about 20 grains (1.296&nbsp;g). [[Edward the Elder]] increased the weight of the English penny to 26 grains (1.685&nbsp;g), thereby aligning it with the penny of [[Charlemagne]].  By the time of the [[Norman conquest of England|Norman Conquest]] (1066), it had decreased to 24 grains (1.555&nbsp;g).  This value was subsequently called the ''[[pennyweight]]'' and formed the basis of the [[Troy weight|Troy units of weight]]—the [[troy ounce]] used to this day for weighting precious metals.<ref name=McGreevy/>{{rp|44–48}} [[Edward I of England|Edward I]] (1272–1307) broke the link between a coin's value and its weight when he debased the English coinage by introducing a [[Groat (coin)|groat]] (four pence) which weighed of 89 grains rather than the expected 96 grains. The groat was further devalued in the 1350s when its weight was reduced to 72 grains.<ref name="Adams">{{cite book
|url = https://archive.org/details/reportuponweight1821unit
|title = Report upon Weights and Measures
|author = Adams, John Quincy
|location = Washington, D.C.
|page = [https://archive.org/details/reportuponweight1821unit/page/29 29]
|publisher =  [[United States Secretary of State|Office of the Secretary of State of the United States]]
|date = 22 February 1821|author-link = John Quincy Adams
}}</ref><ref>{{cite book
|title = Seaby's Standard Catalogue 1972 – British Coins
|publisher = Seaby's Numismatic Publications 
|first1 = H.A.
|last1 = Seaby
|editor1-first = Peter
|editor1-last = Seaby}}</ref>
[[File:BLW Wool Weight with the Royal Arms of England.jpg|thumb|left|upright|Bronze wool weight of {{convert|14|lb|abbr=on}} (1550–1600) stamped with the [[Royal Arms of England|Royal coat of arms]]<br> ([[Victoria and Albert Museum]])]]

During Saxon times land was measured both in terms of its economic value and in terms of its size. The [[Domesday Book]] used the [[Hide (unit)|hide]], an economic unit of measure. In other references the [[furlong]] and the [[rood]] appear to be units related to ploughing procedures. Of particular interest was the rood which was 15 North German feet in length, the North German foot being equivalent to 335&nbsp;mm (13.2&nbsp;inches).<ref name=McGreevy/>{{rp|50}} Craftsmen, on the other hand used a shorter Roman foot. 
[[File:TroyPoundEngraving.jpg|thumb|upright|The standard Troy pound, destroyed in a fire in 1834]]

Standardization of weights and measures was a recurring issue for monarchs. In 965&nbsp;AD, [[Edgar the Peaceful|King Edgar]] decreed "that only one weight and one measure should pass throughout the King's dominion".<ref>{{cite book
|chapter = The History of the English System of Weights and Measures
|first1 = W.J.
|last1 = Owen 
|chapter-url = https://books.google.com/books?id=OjB2dhETxxkC&pg=PA131
|pages = 131
|title = Report of the 50th National Conference on Weights and Measures 1965
|publisher = US Department of Commerce: National Bureau of Standards 
|editor1-first = L.J.
|editor1-last = Chisholm
|date = 1 April 1966
|access-date = 28 May 2013}}</ref> 
In 1197 [[Richard I of England|Richard I]] decreed that the measures of corn and pulse, and of wine and ale should be the same throughout all England.<ref>{{cite book
|url = https://books.google.com/books?id=ccsJeMdOhzkC&q=uniformity+of+weight+richard+1197&pg=PA103
|page = 103
|title = A Source Book for Medieval Economic History
|first1 = Roy Clinton
|last1 = Cave
|first2 = Herbert Henry
|last2 = Coulson
|isbn= 978-0819601452
|lccn = 64-25840
|publisher = Biblo & Tanner
|location = New York
|year = 1965}}</ref> The [[Magna Carta]], signed by [[John, King of England|King John]] in 1215 extended this to include cloth.<ref>{{cite journal
|title = Magna Carta
|year = 1216
|url = https://www.archives.gov/exhibits/featured_documents/magna_carta/translation.html
|access-date = 28 June 2013}}</ref> Some time between 1266 and 1303 the weights and measures of England were radically revised by a law known as the ''[[Composition of Yards and Perches]]'' (''Compositio ulnarum et perticarum'')<ref name="Britain1762">{{cite book|author=Great Britain|title=The statutes at large: from the Magna Charta, to the end of the eleventh Parliament of Great Britain, anno 1761 (continued to 1807)|url=https://books.google.com/books?id=iPQuAAAAIAAJ&q=Compositio+ulnarum+et+perticarum&pg=PA400|volume=1|year=1762|publisher=Printed by J. Bentham|page=400}}</ref> often known as the ''Compositio'' for short. This law, attributed to either Henry III or his successor Edward I, instituted a new foot that was exactly {{frac|10|11}} the length of the old foot, with corresponding reductions in the size of the yard, ell, inch, and barleycorn. (Furlongs remained the same, but the rod changed from 15 old feet to 16{{fraction|1|2}} new feet.<ref name="1977zupko">{{cite book
| last = Zupko
| first = Ronald Edward
| author-link = Ronald Edward Zupko
| title = British Weights and Measures: A History from Antiquity to the Seventeenth Century
| publisher=University of Wisconsin Press
| year = 1977
| isbn = 978-0-299-07340-4
| pages = 6, 10, 20
| url = https://books.google.com/books?id=pWUgAQAAIAAJ&q=millimeters
}}</ref>)

In 1324 [[Edward II of England|Edward II]] systematized units of length by defining the inch as 3 barleycorns, the foot as 12 inches, the yard as 3 feet, the perch as 5{{frac|1|2}} yards, and the acre as an area 4 by 40 perches.<ref name="Smoot">{{cite book
|title = Smoot's Ear: The Measure of Humanity
|first1 = Robert
|last1 = Travenor
|year = 2007
|isbn = 978-0-300-14334-8
|pages = [https://archive.org/details/smootsearmeasure0000tave/page/35 35–36]
|publisher = [[Yale University Press]]
|url = https://archive.org/details/smootsearmeasure0000tave/page/35
}}</ref> Apart from the [[ell]] (45&nbsp;inches or 114.3&nbsp;cm, which continued to be used in the cloth trade) and the [[Chain (unit)|chain]] (introduced by [[Edmund Gunter]] in 1620, and used in land surveying), these units formed the basis of the units of length of the English system of measurement. The units were however redefined many times – during Henry VIII's time standard yards and ells made of [[brass]] were manufactured, during [[Elizabeth I of England|Elizabeth I]]'s time these were replaced with standards made of [[bronze]] and in 1742, after scientific comparisons showed a variation of up to 0.2% from the mean, a definitive standard yard was proposed (but not manufactured).<ref name=McGreevy/>{{rp|122–123}}<ref name="knight">{{cite book|last=Knight|first=Charles|title=The Penny magazine of the Society for the Diffusion of Useful Knowledge|volume=9|year=1840|pages=221–222|publisher=Society for the Diffusion of Useful Knowledge|location=London|url=https://books.google.com/books?id=-BHnAAAAMAAJ}}</ref>

During the medieval era, agricultural products other than wool were mostly sold by volume, with various [[bushel]]s and [[gallon]]s being introduced over the years for different commodities. In the early fourteenth century the wool trade traditionally used the [[avoirdupois]] system of weights, a process that was formalized by [[Edward III of England|Edward III]] in 1340. At the same time, the [[Stone (unit)|stone]], when used to weigh wool, was formalized as being 14&nbsp;pounds.<ref name="McGreevy">{{cite book
|last=McGreevy
|first=Thomas
|title=The Basis of Measurement
|volume=1 Historical Aspects
|isbn=978-0948251825
|publisher = Picton Publishing
|location = Chippenham|year=1995
}}</ref>{{rp|91–94}}

During the [[Tudor period]], numerous reforms were made to English weights and measures. In 1496 [[Henry VII of England|Henry VII]] ordered that reference copies of the yard, pound and gallon should be made of brass and distributed to specified towns and cities throughout the kingdom.<ref name=Kelly/>{{rp|36}} Many weights and measures that had crept into use were banned: in 1527 [[Henry VIII of England|Henry VIII]] banned the [[Tower pound]] (5400 grains against the 5760 grains of the apothecaries and troy pounds) and the [[Pound (mass)#Merchants' pound|mercantile pound]] (6750 grains against the 7000 grains of the pound avoirdupois)<ref name=McGreevy/>{{rp|105}} and in 1592 [[Elizabeth I of England|Elizabeth I]] ordered the use of the "statute mile" (5280 feet against the 5000 feet of the London or Old English mile).<ref name=McGreevy/>{{rp|123}}

Under the [[Acts of Union 1707|Act of Union of 1707]], Scotland, which had developed its own system of weights and measures independently of England, abandoned them in favour of English weights and measures.<ref name=Kelly/>{{rp|90–91}} The [[Acts of Union 1800]] which united Ireland with Great Britain had less of an effect on weights and measures—Irish weights and measures having been based on the English foot and pound avoirdupois since 1351, though the Irish acre and mile were based on a perch of 7 yards, not {{fraction|5|1|2}} yards as in England.<ref name=Kelly/>{{rp|116}}

By the early nineteenth century many commodities had their own set of units, the units of measure for the wool and cloth industries had units of measure specific to those commodities, albeit derived on the pound avoirdupois or the foot while wine and beer used units with the same names but different sizes – the wine gallon being 231 cubic inches and the beer or ale gallon being 282 cubic inches. Agricultural produce was sold by the bushel which was based on yet another gallon – the dry gallon of 268.8 cubic inches. Even though not explicitly permitted by statute, many markets used bushels based on weight rather than volume when selling wheat and barley.<ref name="Kelly">{{cite book
|title = Metrology; or, An exposition of weights and measures
|url = https://books.google.com/books?id=E2kUAAAAQAAJ&q=henry+Viii+weights+measures&pg=PA73
|first1 = Patrick
|last1 = Kelly
|publisher = Lackerington
|year = 1816
|location = London}}</ref>{{rp|85–88}}

== Imperial units ==
{{Main|Imperial units}}
{{Commons category|Imperial units of measure in use in the United Kingdom}}
[[File:Britanski merki za dalzhina Grinuich 2005.jpg|thumb|Public copies of the standard yard and its subdivisions at [[Greenwich Observatory]]]]
The British [[Weights and Measures Acts of the United Kingdom|Weights and Measures Act]] of 1824 repealed all existing British weights and measures legislation, some dating back to the 1300s, and redefined existing units of measure. In particular, a new standard yard and troy pound were manufactured as the standards for length and weight respectively. A new measure, the [[gallon|imperial gallon]], which replaced the many gallons in use,<ref group="Note">[[Thomas Jefferson]], in his ''[[Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States]]'' identified 13 different gallons and 13 different bushels in used in Great Britain in 1790. The gallons ranged from the wine gallon of {{convert|224|cuin|L}} to the beer and ale gallon of {{convert|282|cuin|L}}. The only consistency was 8&nbsp;gallons to the bushel.</ref> was defined as being the volume of 10&nbsp;pounds of water at {{convert|62|°F|°C|abbr=on}} which, after the authorized experiments, was found to be 277.274 cubic inches. The [[bushel]], which like the gallon, had definitions reflecting the various gallons, was defined as 8&nbsp;imperial gallons.<ref name="1824Act">{{cite book
|url = https://books.google.com/books?id=WLouAAAAIAAJ&q=weights&pg=PA339
|pages = 339–354
|title = The Statutes of the United Kingdom of Great Britain and Ireland – 5 George IV 1824
|publisher = His Majesty's Statute and Law Printers
|year = 1824
|location = London
|access-date = 12 June 2013}}</ref><ref name="Poppy">{{cite conference
|url= https://books.google.com/books?id=4F0iAQAAIAAJ&q=Saxon&pg=RA1-PA46
|title = The Development of Weights and Measures Control in the United Kingdom
|first1 = T.G.
|last1 = Poppy
|date= 4 June 1957
|publisher= US Department of Commerce – [[National Institute of Standards and Technology]] (NIST)
|book-title=Report of the National Conference on Weights and Measures, Volumes 41–45
|pages= 22–34
|conference = Forty-second National Conference on Weights and Measures
|location=Washington, D.C.
}}</ref>

The 1824 Act also introduced some changes to the administration of the standards of weights and measures: previously Parliament had been given the custody of the standards but the act passed this responsibility on to the [[Exchequer]]. The act also set up an inspectorate for weights and measures.<ref name=1824Act/><ref name=Poppy/>

The standard yard and pound were lost in 1834 when a fire partially destroyed the Palace of Westminster. Following a report published in 1841 by a commission new standard yard and pound were manufactured using the best available secondary sources. Unlike the previous standard, the new pound standard was a pound avoirdupois. They were accepted by an Act of Parliament as the standards for length and weight in 1855. Following the debacle over the different gallons that had been adopted by the United States and the United Kingdom thirty years earlier, one of the copies of the standard yard was offered to and accepted by the United States Government.<ref name="MacLean">{{cite conference
|url= https://books.google.com/books?id=4F0iAQAAIAAJ&q=weights+measures+act+1951&pg=RA1-PA46
|title = A Central Program for Weights and Measures Canada
|first1 = R.W.
|last1 = MacLean
|date= 4 June 1957
|publisher= US Department of Commerce – [[National Institute of Standards and Technology]] (NIST)
|book-title=Report of the National Conference on Weights and Measures, Volumes 41–45
|pages= 44–49
|conference = Forty-second National Conference on Weights and Measures
|location=Washington, D.C.}}</ref>

The 1835 Weights and Measures Act tidied up a number of shortcomings in the 1825 Act. In response to representations from traders, the [[stone (unit)|stone]] and the [[hundredweight]] were formally defined as being 14&nbsp;pounds and 112&nbsp;pounds respectively and the experiment of defining a "heaped" measure as outlined in the 1824 Act was abandoned.<ref name=Poppy/> Not all trades followed the use of the 14&nbsp;stone—Britten, in 1880 for example, catalogued a number of different values of the stone in various British towns and cities ranging from 4&nbsp;lb to 26&nbsp;lb<ref>{{cite book
|title = A Dictionary of Weights and Measures for the British Isles
|url = https://books.google.com/books?id=0l_k-XMIiQIC&q=stone
|publisher = American Philosophical Society
|year = 1985
|volume = 168
|pages = 391–398
|first1 = Ronald Edward
|last1 = Zupko
|isbn = 9780871691682
}}</ref> The 1835 Act also restricted the use of Troy measure to precious metals and required that coal be sold by weight and not by volume.

[[File:Real Ale 2004-05-09 cropped.jpg|thumb|left|upright|Draught beer is one of the few commodities in the United Kingdom that is still sold by the imperial pint.]]
The Weights and Measures Act of 1878 overhauled the inspection regime of weights and measures used in trade. The act also reaffirmed the use of the brass standard yard and platinum standard pound as the standards for use in the United Kingdom, reaffirmed the use of apothecaries measures in the pharmaceutical industry, reaffirmed the 1824 definition of the gallon, removed the Troy pound from the list of legal units of measure, added the fathom to the list of legal units and fixed the ratio of metric to imperial units at one metre being equal to 39.3708 inches and one kilogram being equal to 15432.3487 grains (1&nbsp;lb = 0.453592654&nbsp;kg).<ref name=Poppy/><ref>{{cite journal
|url = http://legacy.library.ucsf.edu/tid/ysa83a99/pdf
|title = Weights and Measures Act, 1878 [41 & 42 Vict. Ch 49]
|publisher = His Majesty's Stationery Office
|access-date = 16 June 2013}}</ref> Subsequent to the passing of the act, the volume of the gallon which had been defined as being the volume of 10&nbsp;lb distilled water at {{convert|62|°F|°C|lk=on}} was remeasured and set at 277.42 cubic inches though [[HM Customs and Excise]] continued to use the 1824 definition for excise purposes.<ref name=MacLean/>
[[File:Leaving St. Columb - geograph.org.uk - 105130.jpg|thumb|Road distance signs in the United Kingdom use miles.]]

The Weights and Measures Act of 1878 effectively prohibited the use of metric weights for trade, the United Kingdom having declined to sign the [[Metre Convention|Convention of the Metre]] three years previously. The standard imperial yard was not stable – in 1947 its rate of shrinkage was quantified and found to be one part per million every 23 years.<ref name=McGreevy/>{{rp|154}}<ref>{{cite web
|url = http://www.npl.co.uk/educate-explore/factsheets/history-of-length-measurement/
|title = History of Length Measurement
|publisher = [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]]
|access-date = 9 July 2013}}</ref> In April 1884 HJ Chaney, Warden of Standards in London unofficially contacted the [[International Bureau of Weights and Measures|BIPM]] (custodians of the standard metre) inquiring whether the BIPM would calibrate some metre standards that had been manufactured in the United Kingdom. [[Ole Jacob Broch|Broch]], director of the BIPM replied that he was not authorised to perform any such calibrations for non-member states. On 17 September 1884, the British Government signed the convention on behalf of the United Kingdom.<ref>{{cite book
|title = From Artefacts to Atoms: The Bipm and the Search for Ultimate Measurement Standard
|first1 = Terry
|last1 = Quinn
|pages = 133–135
|isbn = 978-0-19-530786-3
|publisher = [[Oxford University Press]]
|year = 2012
|url = https://books.google.com/books?id=jlM907kFhcgC&q=metre++quinn+1883+cipm&pg=PA127}}</ref> The Weights and Measures Act of 1897 authorized the use of metric units for trade; a list of metric to imperial equivalents being published the following year.<ref name="1897Act">{{cite journal
|journal = [[The London Gazette]]
|date = 20 May 1898
|pages = 3135–37
|title = untitled
|number = 26968
}}<br>[http://www.london-gazette.co.uk/issues/26968/pages/3135/page.pdf Page 3135], [http://www.london-gazette.co.uk/issues/26968/pages/3136/page.pdf Page 3136], [http://www.london-gazette.co.uk/issues/26968/pages/3135/page.pdf page 3137]</ref>

Under the Weights and Measures Act of 1824 custody of the standard yard and pound and custody of the administration of weights and measures was entrusted to the [[Exchequer]] but verification was administered locally. The 1835 Act formally described the office and duties of Inspectors of Weights and Measures and required every borough to appoint such officers and the 1866 Act passed responsibility for weights and measures to the [[Board of Trade]]. In 1900 the Board of Trade established the [[National Physical Laboratory (United Kingdom)|National Physical Laboratory]] (NPL) to provide laboratory facilities for weights and measures.<ref name=Poppy/>

After the passage of the 1897 Act, weights and measures in the United Kingdom remained relatively unchanged until after the [[Second World War]]. By the middle of the century the difference of 2 parts per million between the British and US standard yards was causing problems—in 1900 a tolerance of 10 parts per million was adequate for science, but by 1950 this tolerance had shrunk to 0.25 parts per million.<ref name=McGreevy/>{{rp|155}} In 1960 representatives from the NPL and other national laboratories from the United States and Commonwealth agreed to redefine the yard as being exactly 0.9144&nbsp;metres, an action that was ratified by the British Government as part of the 1963 Weights and Measures Act.
[[File:VolumeStandards(AU)-1.JPG|thumb|Standards for the gallon, half gallon, [[quart]] and [[pint]] formerly used in the [[Colony of Victoria]]. Now part of the [[National Archives of Australia]].]]

[[Metrication in the United Kingdom]] began in the mid-1960s. Initially this metrication was voluntary and by 1985 many traditional and imperial units of measure had been voluntarily removed from use in the retail trade. The Weights and Measures Act of 1985 formalized their removal for use in trade, though imperial units were retained for use on road signs and the most common imperial weights such as the foot, inch, pound, ounce, gallon and pint continued to be used in the retail trade for the sale of loose goods or goods measured or weighed in front of the customer.<ref>{{Cite legislation UK
  | type = act
  | year = 1985
  | chapter = 72
  | act = Weights and Measures Act
}}</ref><ref>{{cite book
|title=A Dictionary of Weights, Measures, and Units, 2002
|url=https://archive.org/details/dictionaryofweig0000fenn
|url-access=registration
|editor=Donald Fenna
|publisher=Oxford University Press
|isbn=978-0-19-860522-5
|year=2002}}</ref><ref group="Note">The 1985 Act excluded from use for trade the bushell, cental, chain, drachm, dram, fluid drachm, furlong, grain, hundredweight, ounce apoth., peck, pennyweight, quarter, quintal, rood, scruple, stone, ton, the square mile, cubic inch, cubic foot, cubic yard, and the term 'metric ton'</ref> Since 1 January 2000 it has been unlawful to use imperial units for weights and measures in retail trade in the United Kingdom except as supplementary units or for the sale of draught beer and cider by the pint or milk that is sold in returnable containers.<ref>{{cite web
|url = http://products.ihs.com/Ohsis-SEO/168709.html
|publisher = The Occupational Health & Safety Information Service
|title = SI 1994/2866
|access-date = 29 July 2013
|date = December 1994
|archive-date = 29 October 2013
|archive-url = https://web.archive.org/web/20131029203651/http://products.ihs.com/Ohsis-SEO/168709.html
|url-status = dead
}}</ref>

===British Empire===
When [[British Empire|colonies]] attained [[dominion]] status, they also attained the right to control their own systems of weights and measures.<ref name=MacLean/> Many adopted the imperial system of units with local variations. India<ref name="India">{{cite book
|url = http://lawmin.nic.in/legislative/textofcentralacts/1939.pdf
|title = The Standards of Weight Act, 1939
|work = A Collection of the Acts of the Indian Legislative and of the Governor General for the year 1939
|publisher = Manager of Publications
|location = Delhi
|pages = 223–224
|access-date = 9 July 2013
|archive-url = https://web.archive.org/web/20131029204142/http://lawmin.nic.in/legislative/textofcentralacts/1939.pdf
|archive-date = 29 October 2013
|url-status = dead
}}</ref> and Hong Kong<ref>{{cite web
 |url=http://www.statutelaw.gov.uk/content.aspx?activeTextDocId=2191980 
 |title=Weights and Measures Act 1985 (c. 72) 
 |website=The UK Statute Law Database 
 |publisher=Office of Public Sector Information 
 |quote=§92. 
 |access-date=26 January 2011 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20080912105635/http://www.statutelaw.gov.uk/content.aspx?activeTextDocId=2191980 
 |archive-date=12 September 2008
}}</ref> supplemented the imperial system of units with their own indigenous units of measure, parts of Canada<ref>{{cite web
|url = http://laws-lois.justice.gc.ca/eng/acts/W-6/page-16.html#h-18
|title = Weights and Measures Act 1985, Schedule III, Units of Measure to describe certain land in Quebec
|publisher = Justice Laws Website (Government of Canada)
|access-date = 4 May 2013
|archive-url = https://web.archive.org/web/20130507062539/http://laws-lois.justice.gc.ca/eng/acts/W-6/page-16.html#h-18
|archive-date = 7 May 2013
|url-status = dead
}}</ref> and South Africa<ref>{{cite journal
 |url         = http://www.eepublishers.co.za/images/upload/PostionIT%202011/PositionIT_April_May_2011___SurvT_The%20SA.pdf
 |title       = The South African measurement system and its origin
 |first1      = Tomasz
 |last1       = Zakiewicz
 |journal     = PositionIT
 |date        = April–May 2011
 |access-date  = 4 May 2013
 |pages       = 29–31
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20130317195058/http://www.eepublishers.co.za/images/upload/PostionIT%202011/PositionIT_April_May_2011___SurvT_The%20SA.pdf
 |archive-date = 17 March 2013}}</ref> included land survey units of measure from earlier colonial masters in their systems of measure while many territories used only a subset of the units used in the United Kingdom—in particular the [[stone (unit)|stone]], quarter and cental were not catalogued in, amongst others, Australian,<ref>{{cite web
|title = An Ordinance Relating to Weights and Measures and for other purposes
|year = 1929
|url = http://www.legislation.act.gov.au/a/1929-9/19330801-49042/pdf/1929-9.pdf
|publisher = Australian Capital Territory Publications Counsel
|access-date = 4 May 2013}}</ref> Canadian<ref name=Canada/> and Indian<ref name=India/> legislation. Furthermore, Canada aligned her ton with US measures by cataloguing the ton of 2000&nbsp;lb as being legal for trade, but kept the imperial gallon.<ref name="Canada">{{cite web
|url = http://laws-lois.justice.gc.ca/eng/acts/W-6/page-15.html#docCont
|title = Weights and Measures Act 1985, Schedule II, Canadian Units of Measure
|publisher = Justice Laws Website (Government of Canada)
|access-date = 4 May 2013
|archive-url = https://web.archive.org/web/20141218085852/http://laws-lois.justice.gc.ca/eng/acts/W-6/page-15.html#docCont
|archive-date = 18 December 2014
|url-status = dead
}}</ref>

The standardization of the yard in 1960 required not only agreement between the United States and the United Kingdom, but also of Canada, Australia, New Zealand and South Africa, all of whom had their own standards laboratories.

== United States customary units==
{{main|United States customary units}}
[[File:PoundTroy.jpg|thumb|Pound Troy constructed by the Office of Weights and Measures in the Coast Survey – {{circa}} 1832–1839]]
Prior to the [[United States Declaration of Independence]] in 1776, the [[Thirteen Colonies]] that were to become the United States used the [[English units|English system of measurement]].<ref name=Jefferson/> The [[Articles of Confederation]], which predated the [[Constitution of the United States|Constitution]], gave the central government "the sole and exclusive right and power of...fixing the Standard of Weights and Measures throughout the United States."<ref>{{cite web
|url = http://www.heritage.org/constitution/#!/articles/1/essays/43/weights-and-measures
|title = Weights and Measures
|website = Heritage Guide to the Constitution
|first1 = Edwin
|last1 = Meese III
|first2 = Matthew
|last2 = Spalding
|first3 = David F.
|last3 = Forte
|publisher = The Heritage Foundation
|access-date = 17 April 2013
|year = 2012}}</ref> Subsequent to the formation of the United States, the Constitution reaffirmed the right of Congress to "fix the Standard of Weights and Measures" but reserved the right to regulate commerce and weights and measures to the individual states.<ref name="OurHistory">{{cite web
|url = http://ncwm.net/content/history
|title = Our History
|publisher = [[National Conference on Weights and Measures]]
|access-date = 17 April 2013
|year = 2013
|archive-url = https://web.archive.org/web/20130213154731/http://www.ncwm.net/content/history
|archive-date = 13 February 2013
|url-status = dead
}}</ref>

During the [[1st United States Congress|First Congress of the United States]] in 1789, [[Thomas Jefferson]] was detailed to draw up a plan for the currency and weights of measures that would be used in the new republic. In [[Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States|his 1790 response]] he noted that the existing system of measure was sound but that control of the base artefact was not under the control of the United States. His report suggested a means of manufacturing a local standard and also left the way open for an adoption of a decimal-based system should this be appropriate.<ref name="Jefferson">{{cite web
|url = http://avalon.law.yale.edu/18th_century/jeffplan.asp
|title = Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States
|date = 4 July 1790
|author = Thomas Jefferson
|access-date = 2011-04-19}}</ref> In the event, the existing standards were retained.

[[File:FerdinandHassler.jpg|thumb|left|upright|[[Ferdinand Rudolph Hassler|Ferdinand Hassler]] who acquired standard weights in Europe on behalf of the US Treasury]]
For many years no action was taken at the federal level to ensure harmony in units of measure – the units acquired by the early colonists appeared to serve their purpose. Congress did nothing, but [[Ferdinand Hassler]], Superintendent of the [[US National Geodetic Survey|East Coast survey]], who in 1790 had met using contacts in his native [[Switzerland]] acquired a copy of the [French] ''[[mètre des Archives]]''. 
In 1810 [[Ferdinand Rudolph Hassler|Ferdinand Hassler]] was dispatched to Europe by the Treasury to acquire measuring instruments and standards.<ref name="Hassler">{{cite journal
|journal = Journal of Research of the National Institute of Standards and Technology
|title = A Tale About the First Weights and Measures Intercomparison in the United States in 1832
|volume = 111
|number = 1
|date = January–February 2006
|first1 = Albert C.
|last1 = Parr
|pages = 31–40
|doi=10.6028/jres.111.003|pmid = 27274915
|pmc = 4654608
}}</ref>

In 1827 Albert Gallatin, United States minister at London acquired an "exact copy" of the [[Troy weight|troy pound]] held by the British Government which in 1828 was adopted as the reference copy of weight in the United States.<ref name="NISTCh2">{{cite book
 |chapter-url         = http://physics.nist.gov/Pubs/SP447/sec02.pdf
 |pages       = 2–6
 |chapter     = 2. Early History of Weights and Measures in the United States
 |title       = Weights and Measures Standards of the United States: A brief history – NBS Special Publication 447
 |first1      = Louis E.
 |last1       = Barbrow
 |first2      = Lewis V.
 |last2       = Judson
 |date        = October 1963
 |orig-year    = March 1976
 |lccn        = 76-600055
 |publisher   = US Department of Commerce, National Bureau of Standards
 |access-date  = 19 April 2013
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20131030121602/http://physics.nist.gov/Pubs/SP447/sec02.pdf
 |archive-date = 30 October 2013}}</ref>

In 1821 [[John Quincy Adams]], then [[Secretary of State]] submitted a report based on research commissioned by the Senate in 1817 which recommended against adoption of the metric system. Congress did nothing and in 1832 the Treasury adopted the yard of 36 inches as the unit of length for customs purposes, the avoirdupois pound of 7000 grains as the unit of weight and the gallon of 231 cubic inches (the "Queen Anne gallon") and the bushel of 2150.42 cubic inches as the units of volume.<ref>{{cite book
 |chapter-url         = http://physics.nist.gov/Pubs/SP447/sec04.pdf
 |page        = 6
 |chapter     = 4. Early United States Standards
 |title       = Weights and Measures Standards of the United States: A brief history – NBS Special Publication 447
 |first1      = Louis E.
 |last1       = Barbrow
 |first2      = Lewis V.
 |last2       = Judson
 |date        = October 1963
 |orig-year    = March 1976
 |lccn        = 76-600055
 |publisher   = US Department of Commerce, National Bureau of Standards
 |access-date  = 19 April 2013
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20131030123847/http://physics.nist.gov/Pubs/SP447/sec04.pdf
 |archive-date = 30 October 2013}}</ref> Congress did little to promote standards across the United States other than fixing the size of the yard and the gallon.<ref name="Meese">{{cite web
|url = http://www.heritage.org/constitution/#!/articles/1/essays/43/weights-and-measures
|title = Weights and Measures
|website =  Heritage Guide to the Constitution 
|first1 = Edwin 
|last1 = Meese III
|first2 = Matthew 
|last2 = Spalding
|first3 = David F. 
|last3 = Forte
|publisher = The Heritage Foundation
|access-date = 17 April 2013
|year = 2012}}</ref> 
[[File:Bushel Table of States.jpg|thumb|Nineteenth century list of various bushels by state and commodity]]
Throughout the nineteenth century individual states developed their own standards and in particular a variety of bushels based on weight (mass) rather than volume emerged, dependent on both commodity and state.  This lack of uniformity crippled inter-state trade and in 1905 the National Bureau of Standards called a meeting of the states to discuss the lack of uniform standards and in many cases, a means of regulatory oversight. A meeting was held the following year and subsequently became an annual gathering known as the [[National Conference on Weights and Measures]] (NCWM).  In 1915 the conference published its first model standards.<ref name="OurHistory"/> The bushel was not fully standardized and the [[Chicago Mercantile Exchange]] still (May 2013) uses different bushels for different commodities—a bushel of [[Maize|corn]] being 56&nbsp;lb, a bushel of [[oat]]s 38&nbsp;lb and a bushel of [[soybean]]s 60&nbsp;lb and a bushel of [[Winter wheat|red winter wheat]] (both hard and soft) also 60&nbsp;lb.  Other commodities at the exchange are reckoned in pounds, in short tons or in metric tons.<ref>{{cite web
|url = http://www.cmegroup.com/trading/agricultural/files/AC-225_MetricGuide.pdf
|title = Agricultural Commodity Metric Conversion Guide 
|publisher = [[CME Group]]
|year = 2013
|id = AC225/400/0113
|access-date = 2 May 2013}}</ref>

One of the actions taken by Congress was to permit the use of the metric system in trade (1866), made at the height of the [[metrication]] process in [[Latin America]].<ref>{{cite book
|url = https://archive.org/stream/metricversuseng00boargoog#page/n4/mode/2up
|title=The Metric ''versus'' the English System of Weights and Measures
|id = Research Report Number 42
|date = October 1921
|pages = 12–13
|publisher = National Industrial Conference Board
|access-date = 1 June 2013}}</ref> Other actions were to ratify the [[Metre Convention]] in 1875 and under the [[Mendenhall Order]] of 1897, to redefine the pound and the yard in terms of the [[international prototype of the kilogram]] and the [[international prototype of the metre]] respectively.<ref>{{cite book
 |chapter-url         = http://physics.nist.gov/Pubs/SP447/sec07.pdf
 |chapter     = 7. The Mendenhall Order
 |pages       = 16–20
 |title       = Weights and Measures Standards of the United States: A brief history – NBS Special Publication 447
 |first1      = Louis E.
 |last1       = Barbrow
 |first2      = Lewis V.
 |last2       = Judson
 |date        = October 1963
 |orig-year    = March 1976
 |lccn        = 76-600055
 |publisher   = US Department of Commerce, National Bureau of Standards
 |access-date  = 19 April 2013
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20131030111954/http://physics.nist.gov/Pubs/SP447/sec07.pdf
 |archive-date = 30 October 2013}}</ref>

In 1901 the administration of weights and measures was handed to a federal agency, the National Bureau of Standards, which in 1988 became the National Institute of Standards and Technology.<ref>{{cite journal
|url = https://www.nist.gov/pml/wmd/
|title = Weights and Measures
|journal = NIST
|publisher = [[National Institute of Standards and Technology]] (NIST)
|access-date = 17 April 2013
|year = 2013}}</ref> Inactivity by Congress and the lack of uniformity of weights and measures which were crippling US economic growth in the nineteenth century led to the National Bureau of Standards to call a meeting of states in 1905 which resulted in the setting up of the [[National Conference on Weights and Measures]] (NCWM).<ref>{{cite web
|url = http://www.ncwm.net/about/history
|title = Our History
|publisher = [[National Conference on Weights and Measures]]
|access-date = 4 June 2013
|year = 2013
|archive-date = 21 June 2016
|archive-url = https://web.archive.org/web/20160621105038/https://www.ncwm.net/about/history
|url-status = dead
}}</ref> This organisation is the ''de facto'' controlling body for weights and measures in the United States,<ref>{{cite web
|url = http://www.ncwm.net/about
|title = Setting the United States Standards for Weights and Measures
|publisher = [[National Conference on Weights and Measures]] 
|access-date = 4 June 2013
|year = 2013}}</ref> though in respect of international relations such as membership of the [[General Conference on Weights and Measures]] (an [[intergovernmental organization]]) the US Government itself has to take the lead.<ref>{{cite web
|title = The Metre Convention
|url =  http://www.bipm.org/en/convention/
|publisher = [[International Bureau of Weights and Measures]]
|year = 2013
|access-date = 4 June 2013}}</ref>

During the twentieth century the principal change in the customary system of weights and measures was an agreement between NIST and the corresponding bodies in Australia, Canada, New Zealand, South Africa and the United Kingdom, signed in 1960, that redefined the yard and the pound in terms of the metre and the kilogram respectively.  These new units became known as the international yard and pound. Congress has neither endorsed nor repudiated this action. (See {{section link||Metric equivalents}}).

== Energy, power, and temperature==
{{GravEngAbs}}

Imperial and US customary units have long been used in many branches of engineering. 
Two of the earliest such units of measure to come into use were the ''[[horsepower]]'' and the [[Fahrenheit|''degree Fahrenheit'']]. The ''horsepower'' was defined by [[James Watt]] in 1782 as the power required to raise 33,000 pounds of water through a height of one foot in one minute<ref>{{cite web
|url = http://www.egr.msu.edu/~lira/supp/steam/wattbio.html
|title = Biography of James Watt
|first1 = Carl 
|last1 = Lira 
|publisher = College of Engineering, [[Michigan State University]]
|year = 2012
|access-date = 18 April 2013}}</ref><ref group="Note">The horsepower is now defined as the power required to raise 550 pounds of water a distance of one foot in one second.</ref> and the degree Fahrenheit was first defined by [[Daniel Gabriel Fahrenheit|Daniel Fahrenheit]] in about 1713 as being a temperature scale having its lower calibration point (0&nbsp;°F) at temperature where a supersaturated salt/ice mixture froze and its upper calibration point at body temperature (96&nbsp;°F). In 1777 the [[Royal Society]], under the chairmanship of [[Henry Cavendish]], proposed the definition of the Fahrenheit scale be modified such that the temperature corresponding to the melting point of ice be {{convert|32|°F|°C|abbr=on}} and the boiling point of water under standard atmospheric conditions be {{convert|212|°F|°C|abbr=on}}.

[[File:Old bess steam engine 1777.jpg|thumb|left|[[Old Bess (beam engine)|''Old Bess'']], a 30 HP [[beam engine]] built by [[James Watt]], now preserved in the [[Science Museum, London]].  Watt defined the term ''horsepower''.]]
The [[British thermal unit]] (Btu) is defined as the heat needed to raise the temperature of one pound of water by one degree Fahrenheit.<ref>{{OED|British thermal unit}}</ref> It was in use before 1859 as a unit of heat based on imperial units rather than the metric units used by the French<ref>{{cite journal
|title = History of the British Thermal Unit
|first1 = G.
|last1 = Woledge
|number = 149
|date = 30 May 1942
|doi = 10.1038/149613c0
|page = 613
|bibcode = 1942Natur.149..613W
|volume=149
|journal=Nature|s2cid = 4104904
|doi-access = free
}}</ref>—[[Nicolas Clément|Clément-Desormes]] having defined the [[calorie]] in terms of the kilogram and degrees Celsius ('centigrade') in 1824.<ref>{{cite journal
|journal = Nutrition Journal
|title = Does the history of food energy units suggest a solution to "Calorie confusion"? 
|first1 = James L
|last1 = Hargrove
|date = 17 December 2007
|volume = 6
|doi = 10.1186/1475-2891-6-44
|pmid = 18086303
|pmc = 2238749
|number = 44
|pages=44 
|doi-access = free 
}}</ref>

In 1873 a committee of the [[British Science Association|British Association for the Advancement of Science]] under the chairmanship of [[Lord Kelvin|William Thomson (Lord Kelvin)]] introduced the concept of [[Coherence (units of measurement)|coherence]] into units of measure and proposed the names [[dyne]] and [[erg]] as the units of [[force]] and [[Work (physics)|work]] in the [[Centimetre–gram–second system of units|CGS system of units]].<ref>{{cite journal
|journal = Report on the Forty-third Meeting of the British Association for the Advancement of Science Held at Bradford in September 1873
|year = 1874
|title = First Report of the Committee for the Selection and Nomenclature of Dynamical and Electrical Units
|volume = 43
|editor = Professor Everett
|pages= 222–225
|url = https://www.biodiversitylibrary.org/item/94452
|access-date = 2011-05-10}}</ref><ref>{{cite web
|url = http://www.sizes.com/units/sys_cgs.htm
|title = centimeter-gram-second systems of units
|website = Sizes, Inc
|date = 6 August 2001
|access-date = 2011-04-07}}</ref><ref group="Note">These units are defined as follows:
*The [[dyne]] is the force needed to accelerate a mass of 1&nbsp;g by 1&nbsp;cm/s<sup zoompage-fontsize="9">2</sup>.
*The [[erg]] is the work done when a mass of 1&nbsp;g is moved a distance of 1&nbsp;cm when opposed by a force of 1&nbsp;dyne
Since all the constants in these relationships is unity, the units are said to be [[coherence (units of measurement)|coherent]].</ref> Two years later [[James Thomson (engineer)|James Thomson]], older brother of William Thomson, introduced the term [[poundal]] as a coherent unit of force in the [[Foot–pound–second system]] (FPS) of measurement.<ref>{{OED|poundal}}</ref> The FPS unit of work is the [[foot-poundal]].<ref>{{cite book
|title = Dictionary of Weights, Measures and Units
|first1 = Donald
|last1 = Mena
|publisher = [[Oxford University Press]]
|isbn = 978-0-19-860522-5
|year = 2002
|location = Oxford}}</ref>

Other systems for the measurement of dynamic quantities that used imperial and US customary units are the [[British Gravitational System]] (BG) proposed by [[Arthur Mason Worthington]] and the [[English Engineering Units|English Engineering System]] (EE). Both systems depend on the [[gravitational acceleration]], and use the [[pound-force]] as the unit of force but use different approaches when applying [[Newton's laws of motion]]. In the BG system, force, rather than mass has a [[SI base unit|base unit]] while the [[Slug (unit)|slug]] is a derived unit of [[inertia]] (rather than mass).<ref>{{cite book
|url = https://books.google.com/books?id=-DmfVjBUPksC&q=slug+inertia&pg=PA103
|page = 103
|title = Essentialks of Physics
|volume = 1
|first1 = Sanjay Moreshwar
|last1 = Wagh
|first2 = Dillip Abasaheb
|last2 = Deshpande
|isbn = 978-81-203-4642-0
|location = New Delhi
|publisher = PHI Learning
|year = 2013}}</ref> On the other hand, the EE system uses a different approach and introduces the acceleration due to gravity (''g'') into its equations.  Both these approaches led to slight variations in the meaning of the pound-force (and also of the kilogram-force) in different parts of the world.  Various countries published standard values that should be used for ''g'', and in 1901 the [[General Conference on Weights and Measures|CGPM]] published a standard value for ''g'' that should be used in the "International Service of Weights and Measures", namely {{cvt|9.80665|m/s2|6|order=flip}}, which is equal to the value of ''g'' at 45° latitude.<ref>{{cite web
|url = http://www.calpoly.edu/~gthorncr/ME236/documents/AccuracyofGravity.pdf
|title = How precise is Earth's gravity?
|first1 = Glen
|last1 = Thorncroft
|publisher = Mechanical Engineering Department, [[California Polytechnic State University]]
|location = [[San Luis Obispo, California]]
|access-date = 29 May 2013
|archive-date = 29 October 2013
|archive-url = https://web.archive.org/web/20131029223632/http://www.calpoly.edu/~gthorncr/ME236/documents/AccuracyofGravity.pdf
|url-status = dead
}}</ref>

[[Newton's second law]] in these systems becomes:
:'''BG:''' Force (lbf) = inertia (slugs) × acceleration (ft/s<sup>2</sup>)
:'''EE:''' Force (lbf) = mass (lb) × acceleration (ft/s<sup>2</sup>) ÷ ''g''
:'''AE:''' Force (poundals) = mass (lb) × acceleration (ft/s<sup>2</sup>)

AE is ignored in many engineering courses and textbooks<ref>{{cite web
|title = Concept Review: Unit Systems
|url = http://www.me.mtu.edu/~jstallen/courses/MEEM4200/lectures/energy_intro/Review_unit_systems.pdf
|first1 = Jeffrey S
|last1 = Allen
|type = University course notes
|publisher = [[Michigan Technological University]]
|access-date = 4 May 2013
|archive-url = https://web.archive.org/web/20170517030645/http://www.me.mtu.edu/~jstallen/courses/MEEM4200/lectures/energy_intro/Review_unit_systems.pdf
|archive-date = 17 May 2017
|url-status = dead
}}</ref><ref>{{cite web
|url = http://www.mne.psu.edu/cimbala/Learning/General/units.htm
|title = Dimensions, Units, Conversion Factors, and Significant Digits
|access-date = 4 May 2013
|first1 = John M.
|last1 = Cimbala
|type = University course notes
|publisher = Department of Mechanical and Nuclear Engineering of The [[Pennsylvania State University]]
|date = 6 July 2011
|archive-date = 29 April 2013
|archive-url = https://web.archive.org/web/20130429100658/http://www.mne.psu.edu/cimbala/Learning/General/units.htm
|url-status = dead
}}</ref> while some, such as Darby only uses EE (alongside SI), having described the BG and EE systems as "archaic".<ref>{{cite book
|page = 18
|url = https://books.google.com/books?id=hoXH5qWVnpMC&q=FPS+English+Engineering+Units&pg=PA18
|title = Chemical Engineering Fluid Mechanics
|first1 = Ron 
|last1 = Darby
|isbn = 978-0-8247-0444-5
|publisher = Marcel Dekker
|location = New York
|year = 2001
|access-date = 29 May 2013}}</ref>

==Metric equivalents==
[[File:StandardYardEnd.jpg|thumb|End of the standard yard of 1855 showing the gold plugs which bore the markings for the standard yard]]
The standard yard and [Troy] pound were lost in 1834 when a [[Burning of Parliament|fire partially destroyed the Palace of Westminster]]. Following a report published in 1841 by a commission, a new standard yard and pound were manufactured using the best available secondary sources. Unlike the previous standard, the new pound standard, made of platinum, was a pound avoirdupois. The new yard, slightly longer than a yard to prevent wear as was experienced with the {{lang|fr|[[mètre des Archives]]}}, was made of brass and had two gold plugs close to its end. Scratch marks on the plugs denoted the length of the yard. They were accepted by an Act of Parliament as the standards for length and weight in 1855. Following the debacle over the different gallons that had been adopted by the United States and the United Kingdom thirty years earlier, one of the copies of the standard yard and avoirdupois pound (known in the United States as the "Mint pound") was offered to and accepted by the United States government.<ref name=MacLean/>

In the years that followed the passing of the 1878 act, the standard imperial yard was found to be shrinking at a rate, confirmed in 1950, to be nearly one part per million every 30 years.<ref>{{cite news
|url = https://news.google.com/newspapers?nid=1301&dat=19500608&id=I_dUAAAAIBAJ&pg=1474,1376306
|title = imperial yard shrinking
|date = 8 June 1950
|work= [[The Sydney Morning Herald]]
|access-date = 17 June 2013}}</ref><ref>{{cite news
|url = http://nla.gov.au/nla.news-article83495650
|newspaper = The Daily News
|location = Perth, Australia
|date = 19 January 1931
|title = British Yardstick: Contraction in 80 years – 3 ft still make a yard
|access-date = 18 June 2013}}</ref> On the other hand, the international prototype metre, manufactured from a platinum-iridium alloy rather than brass by a British firm, which in 1889 replaced the {{lang|fr|mètre des Archives}} as the standard for the metre, was found to be more stable than the standard yard.<ref>{{cite web
|url = http://museum.nist.gov/exhibits/ex1/room4b.html
|title = The Mendenhall Order
|website = Virtual Museum
|publisher = NIST
|access-date = 20 June 2013
|archive-url = https://web.archive.org/web/20130730191501/http://museum.nist.gov/exhibits/ex1/room4b.html
|archive-date = 30 July 2013
|url-status = dead
}}</ref> Both the United States and the United Kingdom, as signatories of the [[Metre Convention]], took delivery of copies of both the standard metre and the standard kilogram. The "Mint pound" was also found to be of poor workmanship.

In 1866 the United States government legalised use of metric units in contract law, defining them in terms of the equivalent customary units to five significant figures, which was sufficient for purposes of trade.<ref>{{cite journal
 |title=An Act to authorize the use of the metric system of weights and measures 
 |url=http://lamar.colostate.edu/~hillger/laws/metric-act-bill.html 
 |publisher=39th Congress of the United States 
 |date=18 May 1866 
 |access-date=24 July 2013 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20150705015307/https://lamar.colostate.edu/~hillger/laws/metric-act-bill.html 
 |archive-date=5 July 2015
}}</ref> In 1893, under the [[Mendenhall Order]] the United States abandoned the 1855 yard as a standard of length and the "Mint pound" as a standard of mass, redefining them in terms of the metre and kilogram using the values of the 1866 legislation.<ref>{{cite book
 |last1=Barbrow 
 |first1=Louis E. 
 |last2=Judson 
 |first2=Lewis V. 
 |year=1976 
 |title=Weights and measures standards of the United States: A brief history (NBS Special Publication 447) 
 |location=Washington, D.C. 
 |publisher=Superintendent of Documents, [[NIST]] 
 |access-date=20 June 2013 
 |url=http://physics.nist.gov/Pubs/SP447/ 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20061210014706/http://physics.nist.gov/Pubs/SP447/ 
 |archive-date=10 December 2006 
}}</ref> In the United Kingdom fresh comparisons of the imperial and metric standards of length and mass were made and were used in the [[Weights and Measures Act 1897]] to redefine the yard and pound in terms of the metre and kilogram respectively. In addition, the definitions of both the yard and the pound in terms of the artifacts held by the British government was reaffirmed giving both the yard and the pound two different definitions.<ref name=1897Act/> The differences between the British and the US yard and pound was of the order of a few parts per million. 
{| class="wikitable" style="text-align: center"
|+ Metric Equivalents (1890s) 
|-
!United States<br>[[Mendenhall Order|Mendenhall Order (1893)]]
!United Kingdom<br>[[Weights and Measures Act (1897)]]
!Difference<br>parts per million
|-
| 1 metre = 39.37 inches
| 1 metre = 1.0936143 yards
| 2.9
|-
| 1 kilogram = 2.2046 pounds
| 1 kilogram = 2.2046223 pounds
| 10.1 
|}
By the end of the Second World War, the standards laboratories of Canada, Australia, New Zealand and South Africa also had their own copies of the pound and the yard.  These legal and technical discrepancies, described by McGreevy (pg 290) as being "unsound" led to the Commonwealth Science Conference of 1946.<ref name=MacLean/><ref name="Standards1959">{{cite book
|author=United States. National Bureau of Standards
|author-link=National Institute of Standards and Technology
|title=Research Highlights of the National Bureau of Standards
|url=https://books.google.com/books?id=4aWN-VRV1AoC&pg=PA13
|year=1959
|publisher=US Department of Commerce, National Bureau of Standards
|page=13}}</ref> proposing that the Commonwealth countries and the United States should all redefine the yard and the pound in terms of an agreed fraction of the metre and kilogram respectively. Agreement was reached by the standards laboratories in 1960 to redefine the yard and the pound as 
:1 international yard = {{gaps|0.9144|metres}}
:1 international pound = {{gaps|0.453|592 37|kilograms}}
The final digit of the value chosen for the pound was chosen so as to make the number divisible by 7 without a [[repeating decimal]], making the grain exactly {{gaps|64.798|91|milligrams}}.<ref>{{cite book
 |chapter-url         = http://physics.nist.gov/Pubs/SP447/app5.pdf
 |pages       = 30–31
 |chapter     = Appendix 5. The United States Yard and Pound
 |title       = Weights and Measures Standards of the United States: A brief history – NBS Special Publication 447
 |first1      = Louis E.
 |last1       = Barbrow
 |first2      = Lewis V.
 |last2       = Judson
 |date        = October 1963
 |orig-year    = March 1976
 |lccn        = 76-600055
 |publisher   = US Department of Commerce, National Bureau of Standards
 |access-date  = 20 June 2013
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20130602003918/http://physics.nist.gov/Pubs/SP447/app5.pdf
 |archive-date = 2 June 2013}}</ref>

This agreement was ratified by the United Kingdom in 1963 while Canada pre-empted the decision by adopting these values in 1951, nine years ahead of the full international agreement.  The United States Congress has neither ratified nor repudiated the agreement.<ref name=Meese/>

== Comparison of imperial and US customary systems==
{{main|Comparison of the imperial and US customary measurement systems}}   
[[File:MetricImperialUSCustomaryUnits.jpg|thumb|upright|right|A baby bottle that measures in all three measurement systems—metric, imperial (UK), and US customary.]]
Prior to 1960 the imperial and customary yard and the pound were sufficiently close to each other<ref group="Note">The imperial and customary [[mile]]s differed by about one eighth of an inch and the imperial and customary [[ton|short tons]] by less than an eighth of an ounce.</ref> that for most practical purposes the differences in the sizes of units of length, area, volume and mass could be disregarded, though there were differences in usage - for example, in the United States short road distances are specified in feet<ref>{{cite journal
|url = http://mutcd.fhwa.dot.gov/pdfs/2009r1r2/part2c.pdf
|title = Manual on Uniform Traffic Control Devices: 2009 Edition with Revision Numbers 1 and 2 incorporated, dated May 2012 (PDF)
|page = 132
|publisher = [[United States Department of Transportation]]
|date = 17 July 2013
|access-date = 31 July 2013}}</ref> while in the United Kingdom they are specified in yards<ref>{{Cite legislation UK 
  | type = si
  | year = 2002
  | number = 3113
  | si = The Traffic Signs Regulations and General Directions 2002
}}</ref> The introduction of the international yard in 1960 caused small but noticeable effects in surveying in the United States which resulted in some states retaining the original definitions of the customary units of measure which are now known as the survey mile, foot, while other states adopted the international foot.<ref>{{cite web
|url = http://www.ngs.noaa.gov/INFO/Policy/NAD83FEETPOLICY2.html |title =  Policy of the National Geodetic Survey concerning the Publication of North American Datum of 1983 State Plane Coordinates in feet |date = February 2006 |publisher = [[US National Geodetic Survey|National Geodetic Survey]] |quote = ...legislation which specifically defines the conversion factor, for either the US Survey Foot or the International Foot... |access-date = 29 July 2013}}</ref> According to the [[National Institute of Standards and Technology]], the survey foot is obsolete as of January 1, 2023, and its use is discouraged.<ref name="20200818NYTimes">{{cite web |url=https://www.nytimes.com/2020/08/18/science/foot-surveying-metrology-dennis.html?nl=todaysheadlines&emc=edit_th_20200819 |title=America Has Two Feet. It's About to Lose One of Them. |author=Alanna Mitchell |date=18 August 2020 |work=[[The New York Times]]|access-date=19 August 2020}}</ref>

The definition of units of weight above a pound differed between the customary and the imperial system - the imperial system employed the stone of 14&nbsp;pounds, the hundredweight of 8&nbsp;stone<ref group="Note">In this context, the plural is "stone", not "stones"</ref> and the ton of 2240&nbsp;pounds (20 hundredweight), while the customary system of units did not employ the stone but has a hundredweight of 100&nbsp;pounds and a ton of 2000&nbsp;pounds. In international trade, the ton of 2240&nbsp;pounds was often referred to as the "long ton" and the ton of 2000&nbsp;pounds as the "short ton".  When using customary units, it is usual to express [[body weight]] in pounds, but when using imperial units, to use [[Stone (unit)|stones and pounds]].<ref>{{cite web
|title = Weight Conversion
|publisher = Self Health Company
|location = New Zealand
|year = 2012
 }}</ref><!-- not the best citation, does a better exist?-->

In his ''[[Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States]]'', [[Thomas Jefferson]], then [[United States Secretary of State|secretary of state]], identified 14 different gallons in English statutes varying in size from 224 to 282 cubic inches (3.67 to 4.62 litres).<ref name=Jefferson/>

In 1832, in the absence of any direction by [[United States Congress|Congress]], the [[United States Department of the Treasury|United States Treasury]] chose the second smallest gallon, the "Queen Anne gallon" of 231 cubic inches (3.785 litres), to be the official gallon in the United States for fiscal purposes. Sixteen US fluid ounces make a US pint (8 pints equals 1 gallon in both customary and imperial systems).

During the reform of weights and measures legislation in the United Kingdom in 1824, old gallons were replaced by the new imperial gallon, which was defined to be the volume of 10 pounds of water at 62&nbsp;°F (17&nbsp;°C), and was determined experimentally to be 277.42 cubic inches (4.54609 litres).  Twenty imperial fluid ounces make an imperial pint, the imperial fluid ounce being 0.96 US fluid ounces.

The US Customary system of units makes use of set of dry units of capacity that have a similar set of names<ref group="Note">NIST does not catalogue a "dry gallon" in its list of US units of measure.</ref> to those of liquid capacity, though different volumes: the dry pint having a volume of 33.6 cubic inches (550&nbsp;ml) against the US fluid pint's volume of 28.875 cubic inches (473&nbsp;ml) and the imperial pint of 34.68 cubic inches (568&nbsp;ml). The imperial system of measure does not have an equivalent to the US customary system of "dry measure".

In the international commodities markets, the [[Barrel (unit)|barrel]] ({{gaps|42|US|gallons}}, ≈159&nbsp;litres) is used in both London and New York/Chicago for trading in crude oil and the [[troy ounce]] (≈31.10&nbsp;grams) for trading in precious metals, except the London markets use metric units and the [[Chicago Board of Trade]] uses customary units.

== Units in use ==
The tables below catalogue the imperial units of measure that were permitted for use in trade in the United Kingdom on the eve of metrication (1976)<ref name="1976Act">{{Cite legislation UK 
  | type = act
  | year = 1976
  | chapter = 77
  | act = Weights and Measures &c. Act 1976}}</ref><ref>{{cite legislation UK 
  | type = si
  | year = 1994
  | number = 2867
  | si = The Units of Measurement Regulations 1994}}</ref> and the customary "units of measurement that have traditionally been used in the United States".<ref>{{cite journal
|url = https://www.nist.gov/pml/wmd/pubs/upload/AppC-12-hb44-final.pdf
|at = Appendix C. General Table of Units of Measurement
|publisher = [[National Institute of Standards and Technology]] (NIST)
|title = NIST Handbook 44 – Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices
|year = 2013}}</ref> In addition, named units of measure that are used in the engineering industry are also catalogued. Prior to metrication, the units of measure used in [[Republic of Ireland|Ireland]] were the same as those used in the United Kingdom while those used in the [[British Commonwealth]] and in [[South Africa]] were in most cases a subset of those used in the United Kingdom with, in certain cases, local differences.

Unless otherwise specified, the units of measure quoted below were used in both the United States, the United Kingdom. The SI equivalents are quoted to four significant figures.

===Units of length===
In 1893 the United States fixed the yard at {{fract|3600|3937}} metres, making the yard 0.9144018 metres and 1896 the British authorities fixed the yard as being 0.9143993 metres.{{citation needed|date=January 2019}} At the time the discrepancy of about two parts per million was considered to be insignificant. In 1960, the United Kingdom, United States, Australia, Canada and South Africa standardised their units of length by defining the [[international yard and pound|"international yard"]] as being 0.9144 metres exactly.{{citation needed|date=January 2019}} This change affected land surveyors in the United States and led to the old units being renamed "survey feet", "survey miles" etc.  However the introduction of the metric-based [[Ordnance Survey National Grid]] in the United Kingdom in 1938 meant that British surveyors were unaffected by the change.{{citation needed|date=January 2019}}

{| class="wikitable" style="text-align: center"
|+Linear measure
|-
!Unit
!Abbreviation
!Definition
!SI equivalent
|-
| style="text-align: left" | [[inch]] 
| in  or ″ <ref group="Note" name="2qm">Shall be a double prime symbol, but often approximated as ", a double [[quotation mark]].</ref>
| 25.4&nbsp;mm<ref name="ExactL" group="n">Exact conversion</ref>
|-
| style="text-align: left" | [[Foot (unit)|foot]]
| ft or ′ <ref group="Note" name="1qm">Shall be a [[prime (symbol)|prime symbol]], but often approximated as ', a single quotation mark.</ref>
| 12 inches
| 304.8&nbsp;mm<ref name=ExactL group = n/> 
|-
| style="text-align: left" | [[yard]]
| yd
| 3 feet
| 0.9144&nbsp;m<ref name=ExactL group = n/>
|-
| style="text-align: left" | [[Chain (unit)|chain]]<sup>UK</sup>
| 
| 22&nbsp;yards
| 20.117&nbsp;m
|-
| style="text-align: left" | [[furlong]]<sup>UK</sup>
| fur
| 220 yards
| 201.17&nbsp;m
|-
| style="text-align: left" | [[mile]]<ref group="n">Known as the "international mile" in the United States</ref>
| 
| 1760 yards
| 1609.3&nbsp;m
|}
'''Notes'''
{{Reflist |group = n}}

{| class="wikitable" style="text-align: center"
|+Survey measure (US only)
|-
!Unit
!Abbreviation
!Definition
!SI equivalent
|-
| style="text-align: left" | [[Link (unit)|link]]
| li
| 0.01 chains 
| 201.1&nbsp;mm 
|-
| style="text-align: left" | [[Foot (unit)|survey foot]]
| ft or ′ <ref group=Note name="1qm"/>
| 
| {{fract|1200|3937}}&nbsp;m<ref name="ExactL" group="n">Exact conversion</ref><ref group="n">1 Survey foot ≈ 1.000002 international feet</ref>
|-
| style="text-align: left" | [[Rod (unit)|rod, pole or perch]]
| rd
| {{frac|16|1|2}} feet<ref name="SurveyF" group="n">Survey feet</ref>
| 5.029&nbsp;m
|-
| style="text-align: left" | [[Chain (unit)|chain]]
| ch
| 66&nbsp;feet<ref name=SurveyF group=n/>
| 20.117&nbsp;m
|-
| style="text-align: left" | [[furlong]]
| fur
| 660&nbsp;feet<ref name=SurveyF group=n/>
| 201.17&nbsp;m
|-
| style="text-align: left" | [[mile|US Statute mile]]
| mi
| 5280 feet<ref name=SurveyF group=n/>
| 1609.3&nbsp;m
|}
'''Notes'''
{{Reflist |group = n}}

===Units of area===
The introduction of the international yard in 1960 had no effect on British measurements of area, however US measurements of land area, as opposed to other measurements of area (such as pounds per ''square inch'') continued to be based on the US statute yard.

{| class="wikitable" style="text-align: center"
|+ Area
|-
!Unit
!Abbreviation
!Definition
!SI equivalent
|-
| style="text-align: left" | [[Square foot]]
| sq ft or ft<sup>2</sup>
|
| 0.09290&nbsp;m<sup>2</sup>
|-
| style="text-align: left" | [[Square yard]]
| sq yd or yd<sup>2</sup>
| 9 sq ft
| 0.8361&nbsp;m<sup>2</sup>
|-
| style="text-align: left" | [[Acre]]<sup>UK</sup>
| 
| 4840 sq yd
| 4046&nbsp;m<sup>2</sup>
|-
|}
'''Notes'''
{{Reflist |group = n}}

{| class="wikitable"
|+ Land area in the US
|-
!Unit
!Abbreviation
!Definition
!SI equivalent
|-
| style="text-align: left" | [[Square rod]]
| sq rd or rd<sup>2</sup>
| 272{{fract|1|4}} sq ft<ref name="sqft" group="n">Survey feet</ref>
| 25.29&nbsp;m<sup>2</sup>
|-
| style="text-align: left" | [[Acre]]
|
| {{gaps|43|560}} sq ft<ref group=n name=sqft/>
| 4046&nbsp;m<sup>2</sup>
|-
| style="text-align: left" | [[Square mile]]
| sq mi or mi<sup>2</sup>
| 640 acres
| 2.590&nbsp;km<sup>2</sup>
|-
| style="text-align: left" | [[Survey township|Township]]
|
| style="text-align: left" | 36 sq mi
| style="text-align: left" | 93.24&nbsp;km<sup>2</sup>
|}
'''Notes'''
{{Reflist |group = n}}

===Volume of dry goods===

{| class="wikitable" style="text-align: center"
|+ Dry volume (US)
|-
!Unit
!Abbreviation
!Definition
!SI equivalent
|-
| style="text-align: left" | Cubic inch
| cu in or in<sup>3</sup>
|
| 16.38&nbsp;cm<sup>3</sup>
|-
| style="text-align: left" | Cubic foot
| cu ft or ft<sup>3</sup>
| 1728 cu in
| {{gaps|0.028|31}}&nbsp;m<sup>3</sup>
|-
| style="text-align: left" | Cubic yard
| cu yd or yd<sup>3</sup>
| 27 cu ft
| 0.7646&nbsp;m<sup>3</sup>
|}
'''Notes'''
{{Reflist |group = n}}

{| class="wikitable"
|+ Dry volume (US)
|-
!Unit
!Abbreviation
!Definition
!SI equivalent
|-
| style="text-align: left" | dry pint
| pt
| 33.6 cu in
| 550.6&nbsp;cm<sup>3</sup>
|-
| style="text-align: left" | dry quart
| qt
| 2 pt
| 1.101 L
|-
| style="text-align: left" | dry peck
| pk
| 8 qt
| 8.810 L
|-
| style="text-align: left" | bushel
| bu
| 4 pk 
| 35.24 L
|}
'''Notes'''
{{Reflist |group = n}}

===Volume of liquids===
{| class="wikitable floatright"
|+ Imperial/US gallons
|-
|United States 
| 231 in<sup>3</sup>
| {{val|3.785412|u=L}}
|-
|United Kingdom
| 277.419 in<sup>3</sup>
| {{val|4.54609|u=L}}
|}
Several of the units of liquid volume have similar names, but have different volumes – and in the case of fluid ounces and pints, different relations. In addition the definitions of the imperial and US gallons are based on different concepts – the imperial gallon is defined in terms of the volume occupied by a specified mass of water, while the US gallon is specified in terms of cubic linear measurement.

{| class="wikitable" style="text-align: center"
|+ Volume (UK)
|-
!Unit
!Abbrev
!Definition
!SI equivalent
!US equivalent
|-
| style="text-align: left" | Gallon 
| gal
| colspan=2|{{val|4.54609|u=L}}<ref group="n">This is the definition of the imperial gallon and is therefore exact.</ref>
| 1.201 US gal
|-
| style="text-align: left" | Pint 
| pt
| 1/8 gal
| 568.26&nbsp;ml
| 1.201 US pt
|}

'''Notes'''	
{{Reflist |group = n}}

{| class="wikitable" style="text-align: center"
|+Volume (US)
|-
!Unit
!Abbrev
!Definition
!SI equivalent
!UK equivalent
|-
| style="text-align: left" | Gallon 
| gal
| 231 cu in<ref group="n">This is the definition of the gallon and is therefore exact.</ref>
| 3.785&nbsp;L
| 0.8327 imp gal
|-
| style="text-align: left" | Quart 
| qt
| {{frac|4}} gal
| 946.4&nbsp;mL
| 0.8327 imp qt
|-
| style="text-align: left" | Pint 
| pt
| {{frac|2}} qt
| 473.2&nbsp;mL
| 0.8327 imp pt
|-
| style="text-align: left" | Fluid ounce
| fl oz
| {{frac|16}} pt
| 29.57&nbsp;mL
| 1.041 imp fl oz
|-
| style="text-align: left" | Fluid dram
| fl dr
| {{frac|8}} fl oz
| 3.6967&nbsp;mL
| 1.041 imp fl dr
|-
| style="text-align: left" | Minim
|
| {{frac|60}} fl dr
| 61.61&nbsp;μL
| 1.041 imp fl minim
|}

'''Notes'''	
{{Reflist |group = n}}

===Units of mass===
{| class="wikitable floatright"
|+ Imperial/US pounds
|-
|United States 
|align = left| {{gaps|0.453|592|427|7|kg}}
|-
|United Kingdom
|align = left|{{gaps|0.453|592|338|kg}}
|-
|International
|align = left| {{gaps|0.453|592|37|kg}}
|}
Units of mass in both the imperial and US customary system have always used the same standard, though differences in multiples of the avoirdupois pound developed in the nineteenth century. Both systems used three scales – avoirdupois for general use, troy for precious metals, and apothecaries for medicine.

====Avoirdupois====
{{Main|Avoirdupois}}
{| class="wikitable" style="text-align: center"
|+ Avoirdupois (general use)
|-
!Unit
!Abbreviation
!Definition
!SI equivalent
|-
| style="text-align: left" | Ounce
| oz
| 16 dr<br>{{frac|437|1|2}}&nbsp;gn 
| 28.35&nbsp;g
|-
| style="text-align: left" | Pound
| lb
| 16 oz<br>7000&nbsp;gn
| 453.6&nbsp;g<ref group="n">1 lb is defined as 0.45359237&nbsp;kg</ref>
|-
| style="text-align: left" | Stone<sup>UK</sup>
| st
| 14&nbsp;lb
| 6.350&nbsp;kg
|-
| style="text-align: left" | Ton<sup>US</sup>
|
| 2000&nbsp;lb
| 907.2&nbsp;kg
|}
'''Notes'''
{{Reflist |group = n}}

====Troy====
{{main|Troy weight}}
{| class="wikitable" style="text-align: center"
|+ Troy (precious metals)
|-
!Unit
!Abbreviation
!SI equivalent
|-
| style="text-align: left" | Troy ounce
| oz t
| 31.10&nbsp;g
|}
'''Notes'''
{{Reflist |group = n}}

====Apothecary====
{{main|Apothecaries' system}}
Apothecary mass were used in the [[Pharmacy|pharmaceutical]] industry and have remained almost unchanged since the Middle Ages – the apothecary pound and ounce being the same as the troy pound and ounce, but each system having different divisions. In the United Kingdom, they were replaced by metric units in 1970.<ref>{{cite book
|title = Dictionary of Weights, Measures and Units
|url = https://archive.org/details/dictionaryofweig0000fenn
|url-access = registration
|first1 = Donald
|last1 = Fenna
|publisher = [[Oxford University Press]]
|at = apothecaries scale
|isbn = 978-0-19-860522-5
|year = 2002}}</ref>

{| class="wikitable" style="text-align: center"
|+ Apothecaries (medicinal use)
|-
!Unit
!Abbreviation
!Definition
!SI equivalent
|-
| style="text-align: left" | Grain
|
|
| 64.80&nbsp;mg
|-
| style="text-align: left" | Scruple 
| ℈
| 20 grains
| 1.296&nbsp;g
|-
| style="text-align: left" | Dram 
| ʒ
| 3&nbsp;℈ 
| 3.8879346&nbsp;g
|-
| style="text-align: left" | Ounce 
| ℥
| 8&nbsp;ʒ 
| 31.10&nbsp;g
|-
| style="text-align: left" | Pound 
| {{not a typo|℔}}
| 12 ℥<br>5760 gn
| 373.2&nbsp;g
|}

=== Energy, power, and temperature===
The names of most derived units of measure in the imperial and US customary systems are concatenations of the constituent parts of the unit of measure, for example the unit of pressure is the ''[[Pounds per square inch|pounds [force] per square inch]]''. Apart from the [[poundal]], most of the named units of measure are [[Coherence (units of measurement)|non-coherent]], but were adopted due to traditional working practice.<ref group="Note">For example, [[horsepower]].</ref>

{| class="wikitable"
|+ Energy, power, and temperature
|-
! Quantity
! Unit
! Abbrev
! System
! Definition
! SI equivalent
|-
|Force
|[[poundal]]
|align="center"|pdl
|align="center"|[[Foot–pound–second_system#Absolute_English_System|FPS]]
|Force required to accelerate a mass of one pound-mass by 1&nbsp;ft/s<sup>2</sup>
|align="center"|0.1383 N
|-
|Force
|[[pound force]]
|align="center"|lbf
|align="center"|[[Foot–pound–second_system#British_gravitational_system|BGS]], [[English_Engineering_Units|EEU]]
|Force exerted on a mass of one pound due to gravity
|align="center"|4.448 N
|-
|Mass
|[[Slug (unit)|slug]]
| 
|align="center"|BGS
|mass which, when subjected to a force of one pound-force, accelerates by {{nowrap|1 ft/sec<sup>2</sup>}}
|align="center"|14.59&nbsp;kg
|-
|Mass
|[[Pound (mass)|pound-mass]]
|align="center"|lbm
|align="center"|EEU
|mass which, when subjected to a force of one pound-force, accelerates by {{nowrap|''[[Standard_gravity|g]]'' ft/sec<sup>2</sup>}}<br>(32.17&nbsp;ft/sec<sup>2</sup>)
|align="center"|0.4536&nbsp;kg
|-
|Power
|[[horsepower]]
|align="center"|hp
|align="center"|EEU
|Power required to raise 550&nbsp;lb at the rate of 1&nbsp;ft/s against gravity
|align="center"|745.7&nbsp;W
|-
|Energy
|[[British thermal unit]]
|align="center"|BTU
| align="center"|FPS, BGS, EEU
|Energy required to raise the temperature of 1&nbsp;lb liquid water by {{convert|1|°F-change|°C-change|abbr=on|frac=9}}
|align="center"|1055 J
|-
|Temperature
|[[Fahrenheit|degree Fahrenheit]]
|align="center"|°F
| align="center"|FPS, BGS, EEU
|
|{{nowrap|{{sfrac|9|5}}&nbsp;°C + 32}}
|-
|}

===Other units===
In addition to those catalogued above, there are hundreds of other units of measurement in both the imperial and the US customary system of measurement – many are specific to a particular industry of application. Such units could, in theory, be replaced by general units of the same dimension, for example the [[Barrel (unit)|barrel]] (42 US gallons, 34.97 imperial gallons or 159.0 litres) used in the oil industry has the dimension of volume and could be replaced by the cubic metre or litre.<ref>{{cite book
|title = The Basis of Measurement – Volume 2 – Metrication and Current Practice
|first1 = Thomas
|last1 = McGreevy
|editor1-first = Peter
|editor1-last = Cunningham
|page = 333
|publisher = Picton
|location = Chippenham
|year = 1997
|isbn = 978-0-948251-84-9}}</ref>

The definitions of [[potential difference]] ([[volt]]), [[electric current]] ([[ampere]]), [[electrical resistance]] ([[ohm]]) were defined in terms of metric units, international agreement having been reached at a series of IEC Congress in Chicago between 1881 and 1906 when the electrical industry started.<ref>{{cite book
|title = Systems of Electrical Units
|publisher = US Department of Commenrce
|first1 = Francis B
|last1 = Silsbee
|date = 20 September 1962
|access-date = 17 June 2013
|page = 3
|url = https://digital.library.unt.edu/ark:/67531/metadc70445/m1/9/
|location = Wachington DC}}</ref> At that time, the metric system had become established in continental Europe while an issue in the United Kingdom. Similarly, the radiological units of measurement were defined in terms of metric units, agreement first having been reached at the second International Congress of Radiology at Stockholm (1928).<ref name="ISR_History">{{cite web
 |title       = History
 |first       = Otha W.
 |last        = Linton
 |url         = http://www.isradiology.org/isr/about_02.php
 |access-date  = 24 May 2013
 |publisher   = International Society of Radiology
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20120424025448/http://www.isradiology.org/isr/about_02.php
 |archive-date = 24 April 2012}}</ref>

==Current status==
[[File:Metric_and_imperial_systems_(2019).svg|thumb|Countries using the [[Metric system|metric]], [[Imperial units|imperial]] and [[US customary]] systems as of 2019]]
In the 1960s a [[metrication]] program was initiated in most English-speaking countries, resulting in either the partial or total displacement of the imperial system or the US customary system of measure in those countries. The current status of imperial and US customary units, as summarised by [[National Institute of Standards and Technology|NIST]], is that "the SI metric system is now the official system of units in the United Kingdom, while the customary units are still predominantly used in the United States".<ref name="NISTB">{{cite journal
|url = https://www.nist.gov/pml/wmd/pubs/upload/AppB-12-hb44-final.pdf
|at = Appendix B – Units and Systems of Measurement
|publisher = [[National Institute of Standards and Technology]] (NIST)
|title = NIST Handbook 44 – Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices
|year = 2013}}</ref>

The situation is however not as clear-cut as this. In the United States, for example, the metric system is the predominant system of measure in certain fields such as automobile manufacture even though customary units are used in aircraft manufacture.<ref>{{cite news
|newspaper = [[The New York Times]]
|title = Kinder, Gentler Push for Metric Inches Along
|first1 = Malcolm W.
|last1 = Brownw
|date = 4 June 1996
|url = https://www.nytimes.com/1996/06/04/science/kinder-gentler-push-for-metric-inches-along.html?pagewanted=all&src=pm
|access-date = 8 August 2013}}</ref> In the United Kingdom, metric units are required for almost all regulated <ref group="Note">In this context, "Regulated use" means the uses specified in the ''[http://www.legislation.gov.uk/uksi/2009/3046/pdfs/uksi_20093046_en.pdf Units of Measurement Regulations 2009]'', namely "economic, health, safety, or administrative purposes"</ref> use of units of measure except for a few specifically exempt areas such as [[Road signs in the United Kingdom|road signs]], [[speedometer]]s and [[draught beer]].<ref>{{Cite legislation UK
  | type = si
  | year = 2009
  | number = 3046
  | si = The Units of Measurement Regulations 2009
}}</ref> Metrication is also all but complete in the [[Commonwealth of Nations|Commonwealth]] countries of [[Metrication in Australia|Australia]], [[Metrication in India|India]], [[Metrication in New Zealand|New Zealand]] and South Africa; [[metrication in Canada]] has displaced the imperial system in many areas.<ref>{{cite web
 |url=http://lamar.colostate.edu/~hillger/international.html
 |archive-url=https://web.archive.org/web/20120831004546/http://lamar.colostate.edu/~hillger/international.html
 |url-status=dead
 |archive-date=31 August 2012
 |title=Metric usage and metrication in other countries 
 |publisher=US Metric Association 
 |year=2012 
 |access-date=2 June 2013 
}}</ref>

The imperial and US customary systems of measurement use the [[International system of units|SI]] for their formal definitions, the yard being defined as 0.9144&nbsp;[[metre]]s exactly, the pound avoirdupois as {{val|0.45359237|u=[[kilogram]]s}} exactly while both systems of measure share the definition of the [[second]].

==See also==
* [[Conversion of units]]

==Notes==
{{Reflist|45em|group = Note}}

==References==
{{Reflist|30em}}

{{systems of measurement}}

{{DEFAULTSORT:imperial and US Customary measurement systems}}
[[Category:Customary units of measurement]]
[[Category:Imperial units|*]]
[[Category:Customary units of measurement in the United States| ]]
[[Category:Systems of units]]
[[Category:Units of measurement by country]]
{{Навигационная таблица/Портал/Английская Википедия}}
[[Категория:Английская Википедия]]
[[Категория:Википедия]]
[[Категория:Статья из Википедии]]
[[Категория:Статья из Английской Википедии]]