Imperial and US customary measurement systems
The imperial and US customary measurement systems are both derived from an earlier English system of measurement which in turn can be traced back to Ancient Roman units of measurement, and Carolingian and Saxon units of measure.
The 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 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 colonies).[1] The imperial system of units was developed and used in the United Kingdom and 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
After the
English units of measure
English units of measure, were derived from a combination of Roman, Carolingian and Saxon units of measure. They were a precursor to both the 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.[2]
The earliest records of English units of measure involve the weight (and therefore the value) of
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, 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 mm (13.2 inches).[3]: 50 Craftsmen, on the other hand used a shorter Roman foot.
Standardization of weights and measures was a recurring issue for monarchs. In 965 AD,
In 1324
During the medieval era, agricultural products other than wool were mostly sold by volume, with various bushels and gallons 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 in 1340. At the same time, the stone, when used to weigh wool, was formalized as being 14 pounds.[3]: 91–94
During the
Under the 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.[12]: 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 5+1⁄2 yards as in England.[12]: 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.[12]: 85–88
Imperial units
The British
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.[13][14]
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.[15]
The 1835 Weights and Measures Act tidied up a number of shortcomings in the 1825 Act. In response to representations from traders, the stone and the hundredweight were formally defined as being 14 pounds and 112 pounds respectively and the experiment of defining a "heaped" measure as outlined in the 1824 Act was abandoned.[14] Not all trades followed the use of the 14 stone—Britten, in 1880 for example, catalogued a number of different values of the stone in various British towns and cities ranging from 4 lb to 26 lb[16] 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.
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 lb = 0.453592654 kg).[14][17] Subsequent to the passing of the act, the volume of the gallon which had been defined as being the volume of 10 lb distilled water at 62 °F (17 °C) was remeasured and set at 277.42 cubic inches though HM Customs and Excise continued to use the 1824 definition for excise purposes.[15]
The Weights and Measures Act of 1878 effectively prohibited the use of metric weights for trade, the United Kingdom having declined to sign the 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.[3]: 154 [18] In April 1884 HJ Chaney, Warden of Standards in London unofficially contacted the BIPM (custodians of the standard metre) inquiring whether the BIPM would calibrate some metre standards that had been manufactured in the United Kingdom. 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.[19] 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.[20]
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 (NPL) to provide laboratory facilities for weights and measures.[14]
After the passage of the 1897 Act, weights and measures in the United Kingdom remained relatively unchanged until after the
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.[21][22][Note 2] 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.[23]
British Empire
When colonies attained dominion status, they also attained the right to control their own systems of weights and measures.[15] Many adopted the imperial system of units with local variations. India[24] and Hong Kong[25] supplemented the imperial system of units with their own indigenous units of measure, parts of Canada[26] and South Africa[27] 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, quarter and cental were not catalogued in, amongst others, Australian,[28] Canadian[29] and Indian[24] legislation. Furthermore, Canada aligned her ton with US measures by cataloguing the ton of 2000 lb as being legal for trade, but kept the imperial gallon.[29]
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
Prior to the United States Declaration of Independence in 1776, the Thirteen Colonies that were to become the United States used the English system of measurement.[30] The Articles of Confederation, which predated the Constitution, gave the central government "the sole and exclusive right and power of...fixing the Standard of Weights and Measures throughout the United States."[31] 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.[32]
During the 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 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.[30] In the event, the existing standards were retained.
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
In 1827 Albert Gallatin, United States minister at London acquired an "exact copy" of the troy pound held by the British Government which in 1828 was adopted as the reference copy of weight in the United States.[34]
In 1821
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.[32] The bushel was not fully standardized and the Chicago Mercantile Exchange still (May 2013) uses different bushels for different commodities—a bushel of corn being 56 lb, a bushel of oats 38 lb and a bushel of soybeans 60 lb and a bushel of red winter wheat (both hard and soft) also 60 lb. Other commodities at the exchange are reckoned in pounds, in short tons or in metric tons.[37]
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
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.
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 § Metric equivalents).
Energy, power, and temperature
Base | Force | Weight | Mass | |||||
---|---|---|---|---|---|---|---|---|
2nd law of motion | m = F/a | F = W ⋅ a/g | F = m ⋅ a | |||||
System | BG |
GM | EE | M | AE |
CGS | MTS | SI |
Acceleration (a) | ft/s2 | m/s2 | ft/s2 | m/s2 | ft/s2 | Gal | m/s2 | m/s2 |
Mass (m) | slug | hyl
|
pound-mass | kilogram | pound | gram | tonne | kilogram |
Force (F), weight (W) |
pound | kilopond
|
pound-force | kilopond | poundal | dyne | sthène | newton |
Pressure (p) | pound per square inch | technical atmosphere
|
pound-force per square inch | standard atmosphere | poundal per square foot | barye | pieze |
pascal |
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 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[46][Note 3] and the degree Fahrenheit was first defined by Daniel Fahrenheit in about 1713 as being a temperature scale having its lower calibration point (0 °F) at temperature where a supersaturated salt/ice mixture froze and its upper calibration point at body temperature (96 °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 32 °F (0 °C) and the boiling point of water under standard atmospheric conditions be 212 °F (100 °C).
The British thermal unit (Btu) is defined as the heat needed to raise the temperature of one pound of water by one degree Fahrenheit.[47] It was in use before 1859 as a unit of heat based on imperial units rather than the metric units used by the French[48]—Clément-Desormes having defined the calorie in terms of the kilogram and degrees Celsius ('centigrade') in 1824.[49]
In 1873 a committee of the
Other systems for the measurement of dynamic quantities that used imperial and US customary units are the
- BG: Force (lbf) = inertia (slugs) × acceleration (ft/s2)
- EE: Force (lbf) = mass (lb) × acceleration (ft/s2) ÷ g
- AE: Force (poundals) = mass (lb) × acceleration (ft/s2)
AE is ignored in many engineering courses and textbooks[56][57] while some, such as Darby only uses EE (alongside SI), having described the BG and EE systems as "archaic".[58]
Metric equivalents
The standard yard and [Troy] pound were lost in 1834 when a
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.[59][60] 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 mètre des Archives as the standard for the metre, was found to be more stable than the standard yard.[61] 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.
United States Mendenhall Order (1893) |
United Kingdom Weights and Measures Act (1897)
|
Difference 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.[15][64] 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 = 0.9144metres
- 1 international pound = 0.453592 37kilograms
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 64.79891milligrams.[65]
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.[36]
Comparison of imperial and US customary systems
Prior to 1960 the imperial and customary yard and the pound were sufficiently close to each other[Note 5] 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[66] while in the United Kingdom they are specified in yards[67] 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.[68] According to the National Institute of Standards and Technology, the survey foot is obsolete as of January 1, 2023, and its use is discouraged.[69]
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 pounds, the hundredweight of 8 stone
In his Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States, Thomas Jefferson, then 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).[30]
In 1832, in the absence of any direction by Congress, the 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 °F (17 °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[Note 7] to those of liquid capacity, though different volumes: the dry pint having a volume of 33.6 cubic inches (550 ml) against the US fluid pint's volume of 28.875 cubic inches (473 ml) and the imperial pint of 34.68 cubic inches (568 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
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)
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 3600⁄3937 metres, making the yard 0.9144018 metres and 1896 the British authorities fixed the yard as being 0.9143993 metres.[citation needed] 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" as being 0.9144 metres exactly.[citation needed] 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]
Unit | Abbreviation | Definition | SI equivalent |
---|---|---|---|
inch | in or ″ [Note 8] | 25.4 mm[n 1] | |
foot | ft or ′ [Note 9] | 12 inches | 304.8 mm[n 1] |
yard | yd | 3 feet | 0.9144 m[n 1] |
chainUK | 22 yards | 20.117 m | |
furlongUK | fur | 220 yards | 201.17 m |
mile[n 2] | 1760 yards | 1609.3 m |
Notes
Unit | Abbreviation | Definition | SI equivalent |
---|---|---|---|
link | li | 0.01 chains | 201.1 mm |
survey foot | ft or ′ [Note 9] | 1200⁄3937 m[n 1][n 2] | |
rod, pole or perch | rd | 16+1⁄2 feet[n 3] | 5.029 m |
chain | ch | 66 feet[n 3] | 20.117 m |
furlong | fur | 660 feet[n 3] | 201.17 m |
US Statute mile | mi | 5280 feet[n 3] | 1609.3 m |
Notes
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.
Unit | Abbreviation | Definition | SI equivalent |
---|---|---|---|
Square foot | sq ft or ft2 | 0.09290 m2 | |
Square yard | sq yd or yd2 | 9 sq ft | 0.8361 m2 |
AcreUK | 4840 sq yd | 4046 m2 |
Notes
Unit | Abbreviation | Definition | SI equivalent |
---|---|---|---|
Square rod
|
sq rd or rd2 | 2721⁄4 sq ft[n 1] | 25.29 m2 |
Acre | 43560 sq ft[n 1] | 4046 m2 | |
Square mile | sq mi or mi2 | 640 acres | 2.590 km2 |
Township | 36 sq mi | 93.24 km2 |
Notes
Volume of dry goods
Unit | Abbreviation | Definition | SI equivalent |
---|---|---|---|
Cubic inch | cu in or in3 | 16.38 cm3 | |
Cubic foot | cu ft or ft3 | 1728 cu in | 0.02831 m3 |
Cubic yard | cu yd or yd3 | 27 cu ft | 0.7646 m3 |
Notes
Unit | Abbreviation | Definition | SI equivalent |
---|---|---|---|
dry pint | pt | 33.6 cu in | 550.6 cm3 |
dry quart | qt | 2 pt | 1.101 L |
dry peck | pk | 8 qt | 8.810 L |
bushel | bu | 4 pk | 35.24 L |
Notes
Volume of liquids
United States | 231 in3 | 3.785412 L |
United Kingdom | 277.419 in3 | 4.54609 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.
Unit | Abbrev | Definition | SI equivalent | US equivalent |
---|---|---|---|---|
Gallon | gal | 4.54609 L[n 1] | 1.201 US gal | |
Pint | pt | 1/8 gal | 568.26 ml | 1.201 US pt |
Notes
- ^ This is the definition of the imperial gallon and is therefore exact.
Unit | Abbrev | Definition | SI equivalent | UK equivalent |
---|---|---|---|---|
Gallon | gal | 231 cu in[n 1] | 3.785 L | 0.8327 imp gal |
Quart | qt | 1⁄4 gal | 946.4 mL | 0.8327 imp qt |
Pint | pt | 1⁄2 qt | 473.2 mL | 0.8327 imp pt |
Fluid ounce | fl oz | 1⁄16 pt | 29.57 mL | 1.041 imp fl oz |
Fluid dram | fl dr | 1⁄8 fl oz | 3.6967 mL | 1.041 imp fl dr |
Minim | 1⁄60 fl dr | 61.61 μL | 1.041 imp fl minim |
Notes
- ^ This is the definition of the gallon and is therefore exact.
Units of mass
United States | 0.4535924277kg |
United Kingdom | 0.453592338kg |
International | 0.45359237kg |
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
Unit | Abbreviation | Definition | SI equivalent |
---|---|---|---|
Ounce | oz | 16 dr 437+1⁄2 gn |
28.35 g |
Pound | lb | 16 oz 7000 gn |
453.6 g[n 1] |
StoneUK | st | 14 lb | 6.350 kg |
TonUS | 2000 lb | 907.2 kg |
Notes
- ^ 1 lb is defined as 0.45359237 kg
Troy
Unit | Abbreviation | SI equivalent |
---|---|---|
Troy ounce | oz t | 31.10 g |
Notes
Apothecary
Apothecary mass were used in the 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.[74]
Unit | Abbreviation | Definition | SI equivalent |
---|---|---|---|
Grain | 64.80 mg | ||
Scruple | ℈ | 20 grains | 1.296 g |
Dram | ʒ | 3 ℈ | 3.8879346 g |
Ounce | ℥ | 8 ʒ | 31.10 g |
Pound | ℔ | 12 ℥ 5760 gn |
373.2 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
Quantity | Unit | Abbrev | System | Definition | SI equivalent |
---|---|---|---|---|---|
Force | poundal | pdl | FPS
|
Force required to accelerate a mass of one pound-mass by 1 ft/s2 | 0.1383 N |
Force | pound force
|
lbf | BGS, EEU
|
Force exerted on a mass of one pound due to gravity | 4.448 N |
Mass | slug | BGS | mass which, when subjected to a force of one pound-force, accelerates by 1 ft/sec2 | 14.59 kg | |
Mass | pound-mass | lbm | EEU | mass which, when subjected to a force of one pound-force, accelerates by g ft/sec2 (32.17 ft/sec2) |
0.4536 kg |
Power | horsepower | hp | EEU | Power required to raise 550 lb at the rate of 1 ft/s against gravity | 745.7 W |
Energy | British thermal unit | BTU | FPS, BGS, EEU | Energy required to raise the temperature of 1 lb liquid water by 1 °F (5⁄9 °C) | 1055 J |
Temperature | degree Fahrenheit | °F | FPS, BGS, EEU | 9/5 °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 (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.[75]
The definitions of
Current status
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 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".[78]
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.[79] In the United Kingdom, metric units are required for almost all regulated [Note 11] use of units of measure except for a few specifically exempt areas such as road signs, speedometers and draught beer.[80] Metrication is also all but complete in the Commonwealth countries of Australia, India, New Zealand and South Africa; metrication in Canada has displaced the imperial system in many areas.[81]
The imperial and US customary systems of measurement use the
See also
Notes
- ^ 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 224 cubic inches (3.67 L) to the beer and ale gallon of 282 cubic inches (4.62 L). The only consistency was 8 gallons to the bushel.
- ^ 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'
- ^ The horsepower is now defined as the power required to raise 550 pounds of water a distance of one foot in one second.
- ^ These units are defined as follows:
- The dyne is the force needed to accelerate a mass of 1 g by 1 cm/s2.
- The erg is the work done when a mass of 1 g is moved a distance of 1 cm when opposed by a force of 1 dyne
- ^ The imperial and customary miles differed by about one eighth of an inch and the imperial and customary short tons by less than an eighth of an ounce.
- ^ In this context, the plural is "stone", not "stones"
- ^ NIST does not catalogue a "dry gallon" in its list of US units of measure.
- ^ Shall be a double prime symbol, but often approximated as ", a double quotation mark.
- ^ a b Shall be a prime symbol, but often approximated as ', a single quotation mark.
- ^ For example, horsepower.
- ^ In this context, "Regulated use" means the uses specified in the Units of Measurement Regulations 2009, namely "economic, health, safety, or administrative purposes"
References
- ^ "US leaves the world puzzled by dragging its feet on metric system". The Nation Thailand. 26 December 2015. Retrieved 28 January 2023.
- ^ ISBN 978-0-300-14334-8.
- ^ ISBN 978-0948251825.
- ^ Adams, John Quincy (22 February 1821). Report upon Weights and Measures. Washington, D.C.: Office of the Secretary of State of the United States. p. 29.
- ^ Seaby, H.A. Seaby, Peter (ed.). Seaby's Standard Catalogue 1972 – British Coins. Seaby's Numismatic Publications.
- ^ Owen, W.J. (1 April 1966). "The History of the English System of Weights and Measures". In Chisholm, L.J. (ed.). Report of the 50th National Conference on Weights and Measures 1965. US Department of Commerce: National Bureau of Standards. p. 131. Retrieved 28 May 2013.
- LCCN 64-25840.
- ^ "Magna Carta". 1216. Retrieved 28 June 2013.
{{cite journal}}
: Cite journal requires|journal=
(help) - ^ Great Britain (1762). The statutes at large: from the Magna Charta, to the end of the eleventh Parliament of Great Britain, anno 1761 (continued to 1807). Vol. 1. Printed by J. Bentham. p. 400.
- ISBN 978-0-299-07340-4.
- ^ Knight, Charles (1840). The Penny magazine of the Society for the Diffusion of Useful Knowledge. Vol. 9. London: Society for the Diffusion of Useful Knowledge. pp. 221–222.
- ^ a b c d Kelly, Patrick (1816). Metrology; or, An exposition of weights and measures. London: Lackerington.
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