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Not to be confused with Imperial units.

United States customary units form a system of measurement units commonly used in the United States and U.S. territories since being standardized and adopted in 1832. The United States customary system (USCS or USC) developed from English units which were in use in the British Empire before the U.S. became an independent country. The United Kingdom's system of measures was overhauled in 1824 to create the imperial system, which was officially adopted in 1826, changing the definitions of some of its units. Subsequently, while many U.S. units are essentially similar to their imperial counterparts, there are significant differences between the systems.

Countries using the metric, imperial, and US customary systems as of 2019

The majority of U.S. customary units were redefined in terms of the meter and kilogram with the Mendenhall Order of 1893 and, in practice, for many years before. These definitions were refined by the international yard and pound agreement of 1959.

Americans use customary units in commercial activities, as well as for personal and social use. In science, medicine, many sectors of industry, and some government and military areas, metric units are used. The International System of Units (SI), the modern form of the metric system, is preferred for many uses by the U.S. National Institute of Standards and Technology (NIST). For newer units of measure where there is no traditional customary unit, international units are used, sometimes mixed with customary units; for example, electrical resistance of wire expressed in ohms (SI) per thousand feet.

Contents

The United States system of units of 1832 is based on the system in use in Britain prior to the introduction to the British imperial system on January 1, 1826. Both systems are derived from English units, a system which had evolved over the millennia before American independence, and which had its roots in both Roman and Anglo-Saxon units.

The customary system was championed by the U.S.-based International Institute for Preserving and Perfecting Weights and Measures in the late 19th century. Some advocates of the customary system saw the French Revolutionary, or metric, system as atheistic. The president of an Ohio auxiliary of the Institute wrote that the traditional units were "a just weight and a just measure, which alone are acceptable to the Lord". His organization later went so far as to publish music for a song proclaiming "down with every 'metric' scheme".

The U.S. government passed the Metric Conversion Act of 1975, which made the metric system "the preferred system of weights and measures for U.S. trade and commerce". The legislation states that the federal government has a responsibility to assist industry as it voluntarily converts to the metric system, i.e., metrification. This is most evident in U.S. labeling requirements on food products, where SI units are almost always presented alongside customary units. According to the CIA Factbook, the United States is one of three nations (along with Liberia and Myanmar) that have not adopted the metric system as their official system of weights and measures.

Executive Order 12770, signed by President George H.W. Bush on July 25, 1991, citing the Metric Conversion Act, directed departments and agencies within the executive branch of the United States Government to "take all appropriate measures within their authority" to use the metric system "as the preferred system of weights and measures for United States trade and commerce" and authorized the Secretary of Commerce "to charter an Interagency Council on Metric Policy ("ICMP"), which will assist the Secretary in coordinating Federal Government-wide implementation of this order."

U.S. customary units are widely used on consumer products and in industrial manufacturing. Metric units are standard in science, medicine, as well as many sectors of industry and government, including the military. There are anecdotal objections to the use of metric units in carpentry and the building trades, on the basis that it is easier to remember an integer number of inches plus a fraction than a measurement in millimeters, or that foot-inch measurements are more suitable when distances are frequently divided into halves, thirds and quarters, often in parallel. The metric system also lacks a parallel measure to the foot.

Unit Divisions SI equivalent
Most common measures shown in italics
Exact relationships shown in boldface
International
1 point (p.) 127/360 mm or352.778 μm
1 pica (P.) 12 p. 127/30 mm or4.233 mm
1 inch (in. or ″) 6 P. 25.4 mm
1 foot (ft. or ′) 12 in. 0.3048 m
1 yard (yd.) 3 ft. 0.9144 m
1 mile (mi.) 5280 ft. or 1760 yd. 1.609344 km
US Survey
1 link (li.) 33/50 ft. or 7.92 in. 792/3937 m or20.117 cm
1 (survey) foot (ft.) 1200/3937 m or30.48006 cm
1 rod (rd.) 25 li. or 16.5 ft. 19,800/3937 m or5.029 m
1 chain (ch.) 4 rd. or 66 ft. 79,200/3937 m or20.116 m
1 furlong (fur.) 10 ch. 792/3937 km or201.168 m
1 survey (or statute) mile (mi.) 8 fur. 6336/3937 km or1.609347 km
1 league (lea.) 3 mi. 19,008/3937 km or4.828 km
International Nautical
1 fathom (ftm.) 2 yd. or 6 ft. 1143/625 m or 1.8288 m
1 cable (cb.) 120 ftm. or 1.091 fur. 3429/15625 km or 0.219456 km
1 nautical mile (NM or nmi.) 1.151 mi. or 8.439 cb. 1852 m or 1.852 km

For measuring length, the U.S. customary system uses the inch, foot, yard, and mile, which are the only four customary length measurements in everyday use. Since July 1, 1959, these have been defined on the basis of 1 yard = 0.9144 meters except for some applications in surveying. The U.S., the United Kingdom and other Commonwealth countries agreed on this definition per the International Yard and Pound Agreement of 1958. At the time of the agreement, the basic geodetic datum in North America was the North American Datum of 1927 (NAD27), which had been constructed by triangulation based on the definition of the foot in the Mendenhall Order of 1893, that is 1 foot = 1200/3937 m: this definition was retained for data derived from NAD27, but renamed the US survey foot to distinguish it from the international foot. For most applications, the difference between the two definitions is insignificant – one international foot is exactly 0.999998 of a US survey foot, for a difference of about 1/8 inch (3 mm) per mile – but it affects the definition of the State Plane Coordinate Systems (SPCSs), which can stretch over hundreds of miles.

The NAD27 was replaced in the 1980s by the North American Datum of 1983 (NAD83), which is defined in meters. The SPCSs were also updated, but the National Geodetic Survey left the decision of which (if any) definition of the foot to use to the individual states. All SPCSs are defined in meters, but seven states also have SPCSs defined in US survey feet and the eighth state in international feet: the other 42 states use exclusively metric SPCSs.

State legislation also determines the conversion factor to be used for everyday land surveying and real estate transactions, although the difference (2 ppm) is of no practical significance given the precision of normal surveying measurements over short distances (usually much less than a mile). Twenty-four states have legislated that surveying measures should be based on the US survey foot, eight have legislated that they be made on the basis of the international foot, and eighteen have not specified the conversion factor from metric units.

Unit Divisions SI equivalent
Exact relationships shown in boldface
1 square survey foot (sq. ft. or ft2) 144 square inches 0.09290341 m2
1 square chain (sq. ch. or ch2) 4356 sq. ft. (survey) or 16 sq. rods 404.6873 m2
1 acre 43560 sq. ft. (survey) or 10 sq. ch. 4046.873 m2
1 section 640 acres or 1 sq. mile (survey) 2.589998 km2
1 survey township (twp.) 36 sections or 4 sq. leagues 93.23993 km2

The most widely used area unit with a name unrelated to any length unit is the acre. The National Institute of Standards and Technology contends that customary area units are defined in terms of the square survey foot, not the square international foot. Conversion factors are based on Astin (July 27, 1968) and National Institute of Standards and Technology (2008).

Volume in general
Unit Divisions SI equivalent
1 cubic inch (cu. in.) or (in3) 16.387064 mL
1 cubic foot (cu. ft.) or (ft3) 1728 cu. in. 28.316846592 L
1 cubic yard (cu. yd.) or (yd3) 27 cu. ft. 764.554857984 L
0.764554857984 m3
1 acre-foot (acre-ft.) 43560 cu. ft.
1613.333 cu. yd.
1.23348183754752 ML
1233.482 m3

The cubic inch, cubic foot and cubic yard are commonly used for measuring volume. In addition, there is one group of units for measuring volumes of liquids, and one for measuring volumes of dry material.

Other than the cubic inch, cubic foot, and cubic yard, these units are differently sized from the units in the imperial system, although the names of the units are similar. Also, while the U.S. has separate systems for measuring the volumes of liquids and dry material, the imperial system has one set of units for both.

Fluid volume

Liquid volume
Most common measures shown in italic font

Exact conversions in bold font

Unit Divisions Metric equivalent
1 minim (min.) ≈1 drop or 0.95 grain of water 61.611519921875 μL
1 US fluid dram (fl. dr.) 60 min. 3.6966911953125 mL
1 teaspoon (tsp.) 80 min. 4.92892159375 mL
1 tablespoon (tbsp.) 3 tsp. or 4 fl. dr. 14.78676478125 mL
1 US fluid ounce (fl. oz.) 2 tbsp. or 1.0408 oz. av. of water 29.5735295625 mL
1 US shot (jig.) 1.5 fl. oz. or 3 tbsp. 44.36029434375 mL
1 US gill (gi.) 223 jig or 4 fl. oz. 118.29411825 mL
1 US cup (c.) 2 gi. or 8 fl. oz. 236.5882365 mL
1 (liquid) US pint (pt.) 2 c. or 16.65 oz. av. of water 473.176473 mL
1 (liquid) US quart (qt.) 2 pt. 0.946352946 L
1 (liquid) US pottle (pot.) 2 qt. 1.892705892 L
1 (liquid) US gallon (gal.) 4 qt. or 231 cu. in. 3.785411784 L
1 (liquid) barrel (bbl.) 31.5 gal. or 12 hogshead 119.240471196 L
1 oil barrel (bbl.) 113 (liquid) barrel or 42 gal. or 23 hogshead 158.987294928 L
1 hogshead 1.5 oil barrels or 63 gal. or 8.421875 cu. ft.
or 524.7 lb. of water
238.480942392 L

One US fluid ounce is 116 of a US pint, 132 of a US quart, and 1128 of a US gallon. The teaspoon, tablespoon, and cup are defined in terms of a fluid ounce as 16, 12, and 8 fluid ounces. The fluid ounce derives its name originally from being the volume of one ounce avoirdupois of water, but in the US it is defined as 1128 of a US gallon. Consequently, a fluid ounce of water weighs about 1.041 ounces avoirdupois.

The saying, "a pint's a pound the world around," refers to 16 US fluid ounces of water weighing approximately (about 4% more than) one pound avoirdupois. An imperial pint of water weighs a pound and a quarter (20 oz).

A 23.7 US fl. oz. (700 mL) bottle displaying both U.S. and metric units.

There are varying standards for barrel for some specific commodities, including 31 gallons for beer, 40 gallons for whiskey or kerosene, and 42 gallons for petroleum. The general standard for liquids is 31.5 gal or half a hogshead. The common 55-gallon size of drum for storing and transporting various products and wastes is sometimes confused with a barrel, though it is not a standard measure.

In the U.S., single servings of beverages are usually measured in fluid ounces. Milk is usually sold in half-pints (8 fluid ounces), pints, quarts, half gallons, and gallons. Water volume for sinks, bathtubs, ponds, swimming pools, etc., is usually stated in gallons or cubic feet. Quantities of gases are usually given in cubic feet (at one atmosphere).

Minims, drams, gill, and pottle are rarely used currently. The gill is often referred to as a "half-cup". The pottle is often referred to as a "half-gallon".

Dry volume

Dry volume
Unit Divisions Metric equivalent
1 (dry) pint (pt.) 33.6003125 cu. in. 0.5506104713575 L
1 (dry) quart (qt.) 2 pt. 1.101221 L
1 (dry) gallon (gal.) 4 qt. 4.404884 L
1 peck (pk.) 2 gal. 8.809768 L
1 bushel (bu.) 4 pk. 35.23907016688 L
1 (dry) barrel (bbl.) 7056 cu. in. or3.281 bu. 115.6271 L

Dry volume is measured on a separate system, although many of the names remain the same. Small fruits and vegetables are often sold in dry pints and dry quarts. The US dry gallon is less commonly used, and was not included in the handbook that many states recognize as the authority on measurement law. However pecks, or bushels are sometimes used—particularly for grapes, apples and similar fruits in agricultural regions.

Main articles: Pound (force) and Pound (mass)
Conversions
Type Unit Divisions SI equivalent
Avoirdupois 1 grain (gr.) 17000 lb. 64.79891 mg
1 dram (dr.) 27+1132 gr. or 8.859 carats 1.7718451953125 g
1 ounce (oz) 16 dr. 28.349523125 g
1 pound (lb.) 16 oz. 453.59237 g
1 US hundredweight (cwt.) 100 lb. 45.359237 kg
1 long hundredweight 112 lb. 50.80234544 kg
1 ton (short ton) 20 US cwt. or 2000 lb. 907.18474 kg
1 long ton 20 long cwt. or 2240 lb. 1016.0469088 kg
Troy 1 grain (gr.) 17000 lb. or 15760 lb. t. 64.79891 mg
1 pennyweight (dwt.) 24 gr. or 7.776 carats 1.55517384 g
1 troy ounce (oz. t.) 20 dwt. 31.1034768 g
1 troy pound (lb. t.) 12 oz. t. or 13.17 oz. 373.2417216 g
Most common measures shown in italics

Exact conversions shown in bold

There have historically been five different English systems of mass: tower, apothecaries', troy, avoirdupois, and metric. Of these, the avoirdupois weight is the most common system used in the U.S., although Troy weight is still used to weigh precious metals. Apothecaries weight—once used by pharmacies—has been largely replaced by metric measurements. Tower weight fell out of use in England (due to legal prohibition in 1527) centuries ago, and was never used in the U.S. The imperial system, which is still used for some measures in the United Kingdom and other countries, is based on avoirdupois, with variations from U.S. customary units larger than a pound.

The pound avoirdupois, which forms the basis of the U.S. customary system of mass, is defined as exactly453.59237 grams by agreement between the U.S., the United Kingdom, and other English-speaking countries in 1959. Other units of mass are defined in terms of it.

The avoirdupois pound is legally defined as a measure of mass, but the name pound is also applied to measures of force. For instance, in many contexts, the pound avoirdupois is used as a unit of mass, but in some contexts, the term "pound" is used to refer to "pound-force". The slug is another unit of mass derived from pound-force.

Troy weight, avoirdupois weight, and apothecaries' weight are all built from the same basic unit, the grain, which is the same in all three systems. However, while each system has some overlap in the names of their units of measure (all have ounces and pounds), the relationship between the grain and these other units within each system varies. For example, in apothecary and troy weight, the pound and ounce are the same, but are different from the pound and ounce in avoirdupois in terms of their relationships to grains and to each other. The systems also have different units between the grain and ounce (apothecaries' has scruple and dram, troy has pennyweight, and avoirdupois has just dram, sometimes spelled drachm). The dram in avoirdupois weighs just under half of the dram in apothecaries'. The fluid dram unit of volume is based on the weight of 1 dram of water in the apothecaries' system.

To alleviate confusion, it is typical when publishing non-avoirdupois weights to mention the name of the system along with the unit. Precious metals, for example, are often weighed in "troy ounces", because just "ounce" would be more likely to be assumed to mean an avoirdupois ounce.

For the pound and smaller units, the U.S. customary system and the British imperial system are identical. However, they differ when dealing with units larger than the pound. The definition of the pound avoirdupois in the imperial system is identical to that in the U.S. customary system.

In the U.S., only the ounce, pound and short ton – known in the country simply as the ton – are commonly used, though the hundredweight is still used in agriculture and shipping. The grain is used to describe the mass of propellant and projectiles in small arms ammunition. It was also used to measure medicine and other very small masses.

Grain measures

In agricultural practice, a bushel is a fixed volume of 2,150.42 cubic inches (35.2391 litres). The mass of grain will therefore vary according to density. Some nominal weight examples are;

  • 1 bushel (corn) = 56 lb = 25.4012 kg
  • 1 bushel (wheat) = 60 lb = 27.2155 kg
  • 1 bushel (barley) = 48 lb = 21.7724 kg
Common volume measures in English-speaking countries
(Comparable measures listed for comparison purposes.)
Measure Australia Canada UK US US FDA
Teaspoon 5 mL 5 mL 5 mL 4.93 mL 5 mL
Dessertspoon 10 mL 10 mL
Tablespoon 20 mL 15 mL 15 mL 14.79 mL 15 mL
Fluid ounce 28.41 mL 29.57 mL 30 mL
Cup 250 mL 250 mL 236.59 mL 240 mL
Pint 570 mL 568.26 mL 473.18 mL
Quart 1,136.52 mL 946.35 mL
Gallon 4,546.09 mL 3,785.41 mL

The most common practical cooking measures for both liquid and dry ingredients in the U.S. are the teaspoon, tablespoon, and cup, along with halves, thirds, quarters, and eighths of them. Pounds, ounces, fluid ounces, and common sizes are also used, such as can (presumed size varies depending on product), jar, square (e.g., 1 oz of chocolate), stick (e.g., 4 oz butter), or fruit/vegetable (e.g., a half lemon, two medium onions).[citation needed]

Degrees Fahrenheit are used in the U.S. to measure temperatures in most non-scientific contexts. The Rankine scale of absolute temperature also saw some use in thermodynamics. Scientists worldwide use the kelvin and degree Celsius. Several U.S. technical standards are expressed in Fahrenheit temperatures, and some American medical practitioners use degrees Fahrenheit for body temperature.

The relationship between the different temperature scales is linear but the scales have different zero points, so conversion is not simply multiplication by a factor. Pure water freezes at 32 °F = 0 °C and boils at 212 °F = 100 °C at 1 atm. The conversion formula is:

[ F ] = 9 5 [ C ] + 32 {\displaystyle [^{\circ }{\text{F}}]={\tfrac {9}{5}}[^{\circ }{\text{C}}]+32}

or inversely as

[ C ] = 5 9 ( [ F ] 32 ) . {\displaystyle [^{\circ }{\text{C}}]={\tfrac {5}{9}}{\bigl (}[^{\circ }{\text{F}}]-32{\bigr )}.}

Length

Volume

Mass

  • 1 slug = 1 lbf⋅s2/ft ≈ 14.59390 kg

Force

  • 1 poundal = force to accelerate 1 pound mass 1 foot/second/second ≈ 0.138 Newtons.
  • 1 kip = 1000 lbf ≈ 4.44822 kN

Energy

Power

Pressure

Torque

Insulation

  • 1 R-value (ft2⋅°F⋅h/Btu) ≈ 0.1761 RSI (K⋅m2/W)

Various combination units are in common use; these are straightforwardly defined based on the above basic units.

Sizing systems are used for various items in commerce, several of which are U.S.-specific:

The United States Code refers to these units as "traditional systems of weights and measures".

Other common ways of referring to the system are: customary, standard, or, erroneously, English, or imperial (which refers to the post-1824 reform measures used throughout the British Empire & Commonwealth countries). Another term is the foot–pound–second (FPS) system, as opposed to centimeter–gram–second (CGS) and meter–kilogram–second (MKS) systems.

Tools and fasteners with sizes measured in inches are sometimes called "SAE bolts" or "SAE wrenches" to differentiate them from their metric counterparts. The Society of Automotive Engineers (SAE) originally developed fasteners standards using U.S. units for the U.S. auto industry; the organization now uses metric units.

  1. Barbrow, L.E. and Judson, L. V. (1976) Weights and Measures of the United States. National Bureau of Standards Special Publication 447. p. 5–6
  2. T.C. Mendenhall, Superintendent of Standard Weights and Measures. Order of April 5, 1893 Archived September 30, 2012, at the Wayback Machine, published as Appendix 6 to the Report for 1893 of the Coast and Geodetic Survey.
  3. Astin, A.V., Karo, H.A. and Mueller, F.H. (June 25, 1959). Doc 59-5442, "Refinement of Values for the Yard and the Pound." Federal Register. Note that 999,998 = 3937 × 254.
  4. Laws and Metric Program. U.S. National Institute of Standards and Technology, 2010
  5. "English units of measurement". The Columbia Encyclopedia 6th ed. 2001-2007. archived copy.
  6. Martin Gardner (May 4, 2012). Fads and Fallacies in the Name of Science. Courier Corporation. pp. 180–. ISBN 978-0-486-13162-7.
  7. "References - Weights and Measures". The World Factbook. Washington, D.C.: Central Intelligence Agency. RetrievedApril 22, 2021.
  8. Robyn Williams (February 8, 1998) "Trouble with the Metric System". Australian Radio National, Ockham's Razor.
  9. Ed Tenner, (May 2005). "The Trouble with the Meter". Technologyreview.com.
  10. Roberts, R.W. (February 3, 1975). Federal Register republished in Barbrow, L.E. and Judson, L. V. (1976) Weights and Measures of the United States. National Bureau of Standards Special Publication 447. p. 36
  11. Barton, John W.; Bowers, Shelby L.; Butcher, Tina G, Harshman, Richard A.; Lee, G. Diane & Warfield, Lisa, eds. Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices 2022 Edition. n.p.: National Institute of Standards and Technology. pages B-7, C-20.
  12. "Frequently Asked Questions about the National Geodetic Survey". National Geodetic Survey. RetrievedMay 16, 2009.
  13. Astin, A. V. (July 27, 1968). Federal Register Archived October 5, 2006, at the Wayback Machine. Republished in Barbrow, L.E and Judson, L.V. Weights and Measures of the United States: A Brief History. National Bureau of Standards Special Publication 447. pp. 34–35.
  14. National Institute of Standards and Technology. (2008). Guide for the Use of the International System of Units (SI).
  15. The recommended symbol for the liter in the United States is 'L' per National Institute of Standards and Technology. (1995.) Guide for the Use of the International System of Units (SI). Special Publication 811.
  16. 101st Conference on Weights and Measures 2016. (2017). Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. National Institute of Standards and Technology. p. C-6, C-11, C-16.
  17. Summary of State Laws and Regulations in Weights and Measures Archived December 5, 2011, at the Wayback Machine. (2005) National Institute of Standards and Technology.
  18. NIST Handbook 44, Appendix C, General Tables of Units of Measurement, page C-6 Avoirdupois Units of Mass Archived October 18, 2011, at the Wayback Machine
  19. "United States Department of Agriculture". United States Department of Agriculture. August 20, 2019. RetrievedMay 28, 2020.
  20. "Weights and Measures of agricultural commodities"(PDF). United States Department of Agriculture-National Agricultural Statistics Service. RetrievedMay 28, 2020.
  21. "Title 21, 101.9 Nutrition labeling of food"(PDF). Code of Federal Regulations. US Government Printing Office. April 12, 2012. RetrievedNovember 2, 2014. For nutrition labeling purposes, a teaspoon means 5 milliliters (mL), a tablespoon means 15 mL, a cup means 240 mL, 1 fl oz means 30 mL, and 1 oz in weight means 28 g.
  22. Wells, Larry J. (1981). Makin' Leather: A Manual of Primitive and Modern Leather Skills. Cedar Fort. p. 13. ISBN 0882908359.
  23. 15 U.S.C. § 205b
  24. "Rules for SAE Use of SI (Metric) Units"(PDF). Society of Automotive Engineers, Inc. May 1999. RetrievedJuly 1, 2012.

United States customary units Article Talk Language Watch Edit Not to be confused with Imperial units United States customary units form a system of measurement units commonly used in the United States and U S territories since being standardized and adopted in 1832 1 The United States customary system USCS or USC developed from English units which were in use in the British Empire before the U S became an independent country The United Kingdom s system of measures was overhauled in 1824 to create the imperial system which was officially adopted in 1826 changing the definitions of some of its units Subsequently while many U S units are essentially similar to their imperial counterparts there are significant differences between the systems Countries using the metric imperial and US customary systems as of 2019 The majority of U S customary units were redefined in terms of the meter and kilogram with the Mendenhall Order of 1893 and in practice for many years before 2 These definitions were refined by the international yard and pound agreement of 1959 3 Americans use customary units in commercial activities as well as for personal and social use In science medicine many sectors of industry and some government and military areas metric units are used The International System of Units SI the modern form of the metric system is preferred for many uses by the U S National Institute of Standards and Technology NIST 4 For newer units of measure where there is no traditional customary unit international units are used sometimes mixed with customary units for example electrical resistance of wire expressed in ohms SI per thousand feet Contents 1 History 2 Length 3 Area 4 Volume 4 1 Fluid volume 4 2 Dry volume 5 Mass and weight 5 1 Grain measures 6 Cooking measures 7 Temperature 8 Other units 9 Other names for U S customary units 10 See also 11 References 12 External linksHistory EditSee also Imperial and US customary measurement systems and Comparison of the imperial and US customary measurement systems The United States system of units of 1832 is based on the system in use in Britain prior to the introduction to the British imperial system on January 1 1826 5 Both systems are derived from English units a system which had evolved over the millennia before American independence and which had its roots in both Roman and Anglo Saxon units The customary system was championed by the U S based International Institute for Preserving and Perfecting Weights and Measures in the late 19th century Some advocates of the customary system saw the French Revolutionary or metric system as atheistic The president of an Ohio auxiliary of the Institute wrote that the traditional units were a just weight and a just measure which alone are acceptable to the Lord His organization later went so far as to publish music for a song proclaiming down with every metric scheme 6 The U S government passed the Metric Conversion Act of 1975 which made the metric system the preferred system of weights and measures for U S trade and commerce The legislation states that the federal government has a responsibility to assist industry as it voluntarily converts to the metric system i e metrification This is most evident in U S labeling requirements on food products where SI units are almost always presented alongside customary units According to the CIA Factbook the United States is one of three nations along with Liberia and Myanmar that have not adopted the metric system as their official system of weights and measures 7 Executive Order 12770 signed by President George H W Bush on July 25 1991 citing the Metric Conversion Act directed departments and agencies within the executive branch of the United States Government to take all appropriate measures within their authority to use the metric system as the preferred system of weights and measures for United States trade and commerce and authorized the Secretary of Commerce to charter an Interagency Council on Metric Policy ICMP which will assist the Secretary in coordinating Federal Government wide implementation of this order U S customary units are widely used on consumer products and in industrial manufacturing Metric units are standard in science medicine as well as many sectors of industry and government including the military 7 There are anecdotal objections to the use of metric units in carpentry and the building trades on the basis that it is easier to remember an integer number of inches plus a fraction than a measurement in millimeters 8 or that foot inch measurements are more suitable when distances are frequently divided into halves thirds and quarters often in parallel The metric system also lacks a parallel measure to the foot 9 Length EditUnit Divisions SI equivalentMost common measures shown in italics Exact relationships shown in boldfaceInternational1 point p 127 360 mm or 352 778 mm1 pica P 12 p 127 30 mm or 4 233 mm1 inch in or 6 P 25 4 mm1 foot ft or 12 in 0 3048 m 10 1 yard yd 3 ft 0 9144 m1 mile mi 5280 ft or 1760 yd 1 609344 kmUS Survey1 link li 33 50 ft or 7 92 in 792 3937 m or 20 117 cm1 survey foot ft 1200 3937 m or 30 48006 cm 10 1 rod rd 25 li or 16 5 ft 19 800 3937 m or 5 029 m1 chain ch 4 rd or 66 ft 79 200 3937 m or 20 116 m1 furlong fur 10 ch 792 3937 km or 201 168 m1 survey or statute mile mi 8 fur 6336 3937 km or 1 609347 km 10 1 league lea 3 mi 19 008 3937 km or 4 828 km 11 International Nautical 10 1 fathom ftm 2 yd or 6 ft 1143 625 m or 1 8288 m1 cable cb 120 ftm or 1 091 fur 3429 15625 km or 0 219456 km1 nautical mile NM or nmi 1 151 mi or 8 439 cb 1852 m or 1 852 km For measuring length the U S customary system uses the inch foot yard and mile which are the only four customary length measurements in everyday use Since July 1 1959 these have been defined on the basis of 1 yard 0 9144 meters except for some applications in surveying 3 The U S the United Kingdom and other Commonwealth countries agreed on this definition per the International Yard and Pound Agreement of 1958 At the time of the agreement the basic geodetic datum in North America was the North American Datum of 1927 NAD27 which had been constructed by triangulation based on the definition of the foot in the Mendenhall Order of 1893 that is 1 foot 1200 3937 m this definition was retained for data derived from NAD27 but renamed the US survey foot to distinguish it from the international foot 3 For most applications the difference between the two definitions is insignificant one international foot is exactly 0 999998 of a US survey foot for a difference of about 1 8 inch 3 mm per mile but it affects the definition of the State Plane Coordinate Systems SPCSs which can stretch over hundreds of miles 12 The NAD27 was replaced in the 1980s by the North American Datum of 1983 NAD83 which is defined in meters The SPCSs were also updated but the National Geodetic Survey left the decision of which if any definition of the foot to use to the individual states All SPCSs are defined in meters but seven states also have SPCSs defined in US survey feet and the eighth state in international feet the other 42 states use exclusively metric SPCSs 12 State legislation also determines the conversion factor to be used for everyday land surveying and real estate transactions although the difference 2 ppm is of no practical significance given the precision of normal surveying measurements over short distances usually much less than a mile Twenty four states have legislated that surveying measures should be based on the US survey foot eight have legislated that they be made on the basis of the international foot and eighteen have not specified the conversion factor from metric units 12 Area EditUnit Divisions SI equivalentExact relationships shown in boldface1 square survey foot sq ft or ft2 144 square inches 0 092903 41 m21 square chain sq ch or ch2 4356 sq ft survey or 16 sq rods 404 6873 m21 acre 43560 sq ft survey or 10 sq ch 4046 873 m21 section 640 acres or 1 sq mile survey 2 589998 km21 survey township twp 36 sections or 4 sq leagues 93 23993 km2 The most widely used area unit with a name unrelated to any length unit is the acre The National Institute of Standards and Technology contends that customary area units are defined in terms of the square survey foot not the square international foot 10 Conversion factors are based on Astin July 27 1968 13 and National Institute of Standards and Technology 2008 14 Volume EditVolume in generalUnit Divisions SI equivalent1 cubic inch cu in or in3 16 387064 mL 15 1 cubic foot cu ft or ft3 1728 cu in 28 316846 592 L1 cubic yard cu yd or yd3 27 cu ft 764 554857 984 L 0 764554 857 984 m31 acre foot acre ft 43560 cu ft 1613 333 cu yd 1 233481 837 547 52 ML 1233 482 m3 The cubic inch cubic foot and cubic yard are commonly used for measuring volume In addition there is one group of units for measuring volumes of liquids and one for measuring volumes of dry material Other than the cubic inch cubic foot and cubic yard these units are differently sized from the units in the imperial system although the names of the units are similar Also while the U S has separate systems for measuring the volumes of liquids and dry material the imperial system has one set of units for both Fluid volume Edit Liquid volumeMost common measures shown in italic font Exact conversions in bold fontUnit Divisions Metric equivalent1 minim min 1 drop or 0 95 grain of water 61 611519 921 875 mL1 US fluid dram fl dr 60 min 3 696691 195 3125 mL1 teaspoon tsp 80 min 4 928921 593 75 mL1 tablespoon tbsp 3 tsp or 4 fl dr 14 786764 781 25 mL1 US fluid ounce fl oz 2 tbsp or 1 0408 oz av of water 29 573529 5625 mL1 US shot jig 1 5 fl oz or 3 tbsp 44 360294 343 75 mL1 US gill gi 22 3 jig or 4 fl oz 118 294118 25 mL1 US cup c 2 gi or 8 fl oz 236 5882365 mL1 liquid US pint pt 2 c or 16 65 oz av of water 473 176473 mL1 liquid US quart qt 2 pt 0 946352 946 L1 liquid US pottle pot 2 qt 1 892705 892 L1 liquid US gallon gal 4 qt or 231 cu in 3 785411 784 L1 liquid barrel bbl 31 5 gal or 1 2 hogshead 119 240471 196 L1 oil barrel bbl 11 3 liquid barrel or 42 gal or 2 3 hogshead 158 987294 928 L1 hogshead 1 5 oil barrels or 63 gal or 8 421875 cu ft or 524 7 lb of water 238 480942 392 L One US fluid ounce is 1 16 of a US pint 1 32 of a US quart and 1 128 of a US gallon The teaspoon tablespoon and cup are defined in terms of a fluid ounce as 1 6 1 2 and 8 fluid ounces The fluid ounce derives its name originally from being the volume of one ounce avoirdupois of water but in the US it is defined as 1 128 of a US gallon Consequently a fluid ounce of water weighs about 1 041 ounces avoirdupois The saying a pint s a pound the world around refers to 16 US fluid ounces of water weighing approximately about 4 more than one pound avoirdupois An imperial pint of water weighs a pound and a quarter 20 oz A 23 7 US fl oz 700 mL bottle displaying both U S and metric units There are varying standards for barrel for some specific commodities including 31 gallons for beer 40 gallons for whiskey or kerosene and 42 gallons for petroleum The general standard for liquids is 31 5 gal or half a hogshead The common 55 gallon size of drum for storing and transporting various products and wastes is sometimes confused with a barrel though it is not a standard measure In the U S single servings of beverages are usually measured in fluid ounces Milk is usually sold in half pints 8 fluid ounces pints quarts half gallons and gallons Water volume for sinks bathtubs ponds swimming pools etc is usually stated in gallons or cubic feet Quantities of gases are usually given in cubic feet at one atmosphere Minims drams gill and pottle are rarely used currently The gill is often referred to as a half cup The pottle is often referred to as a half gallon Dry volume Edit Dry volume 16 Unit Divisions Metric equivalent1 dry pint pt 33 6003125 cu in 0 550610 471 3575 L1 dry quart qt 2 pt 1 101221 L1 dry gallon gal 4 qt 4 404884 L1 peck pk 2 gal 8 809768 L1 bushel bu 4 pk 35 239070 166 88 L1 dry barrel bbl 7056 cu in or 3 281 bu 115 6271 L Dry volume is measured on a separate system although many of the names remain the same Small fruits and vegetables are often sold in dry pints and dry quarts The US dry gallon is less commonly used and was not included in the handbook that many states recognize as the authority on measurement law 16 17 However pecks or bushels are sometimes used particularly for grapes apples and similar fruits in agricultural regions Mass and weight EditMain articles Pound force and Pound mass Conversions Type Unit Divisions SI equivalentAvoirdupois 1 grain gr 1 7000 lb 64 79891 mg1 dram dr 27 11 32 gr or 8 859 carats 1 771845 195 3125 g1 ounce oz 16 dr 28 349523 125 g1 pound lb 16 oz 453 59237 g1 US hundredweight cwt 100 lb 45 359237 kg1 long hundredweight 112 lb 50 802345 44 kg1 ton short ton 20 US cwt or 2000 lb 907 18474 kg1 long ton 20 long cwt or 2240 lb 1016 0469088 kgTroy 1 grain gr 1 7000 lb or 1 5760 lb t 64 79891 mg1 pennyweight dwt 24 gr or 7 776 carats 1 555173 84 g1 troy ounce oz t 20 dwt 31 1034768 g1 troy pound lb t 12 oz t or 13 17 oz 373 2417216 gMost common measures shown in italics Exact conversions shown in bold There have historically been five different English systems of mass tower apothecaries troy avoirdupois and metric Of these the avoirdupois weight is the most common system used in the U S although Troy weight is still used to weigh precious metals Apothecaries weight once used by pharmacies has been largely replaced by metric measurements Tower weight fell out of use in England due to legal prohibition in 1527 centuries ago and was never used in the U S The imperial system which is still used for some measures in the United Kingdom and other countries is based on avoirdupois with variations from U S customary units larger than a pound The pound avoirdupois which forms the basis of the U S customary system of mass is defined as exactly 453 59237 grams by agreement between the U S the United Kingdom and other English speaking countries in 1959 Other units of mass are defined in terms of it The avoirdupois pound is legally defined as a measure of mass 18 but the name pound is also applied to measures of force For instance in many contexts the pound avoirdupois is used as a unit of mass but in some contexts the term pound is used to refer to pound force The slug is another unit of mass derived from pound force Troy weight avoirdupois weight and apothecaries weight are all built from the same basic unit the grain which is the same in all three systems However while each system has some overlap in the names of their units of measure all have ounces and pounds the relationship between the grain and these other units within each system varies For example in apothecary and troy weight the pound and ounce are the same but are different from the pound and ounce in avoirdupois in terms of their relationships to grains and to each other The systems also have different units between the grain and ounce apothecaries has scruple and dram troy has pennyweight and avoirdupois has just dram sometimes spelled drachm The dram in avoirdupois weighs just under half of the dram in apothecaries The fluid dram unit of volume is based on the weight of 1 dram of water in the apothecaries system To alleviate confusion it is typical when publishing non avoirdupois weights to mention the name of the system along with the unit Precious metals for example are often weighed in troy ounces because just ounce would be more likely to be assumed to mean an avoirdupois ounce For the pound and smaller units the U S customary system and the British imperial system are identical However they differ when dealing with units larger than the pound The definition of the pound avoirdupois in the imperial system is identical to that in the U S customary system In the U S only the ounce pound and short ton known in the country simply as the ton are commonly used though the hundredweight is still used in agriculture and shipping The grain is used to describe the mass of propellant and projectiles in small arms ammunition It was also used to measure medicine and other very small masses Grain measures Edit In agricultural practice a bushel is a fixed volume of 2 150 42 cubic inches 35 2391 litres The mass of grain will therefore vary according to density Some nominal weight examples are 19 20 1 bushel corn 56 lb 25 4012 kg 1 bushel wheat 60 lb 27 2155 kg 1 bushel barley 48 lb 21 7724 kgCooking measures EditCommon volume measures in English speaking countries Comparable measures listed for comparison purposes Measure Australia Canada UK US US FDA 21 Teaspoon 5 mL 5 mL 5 mL 4 93 mL 5 mLDessertspoon 10 mL 10 mL Tablespoon 20 mL 15 mL 15 mL 14 79 mL 15 mLFluid ounce 28 41 mL 29 57 mL 30 mLCup 250 mL 250 mL 236 59 mL 240 mLPint 570 mL 568 26 mL 473 18 mL Quart 1 136 52 mL 946 35 mL Gallon 4 546 09 mL 3 785 41 mL Main article Cooking weights and measures The most common practical cooking measures for both liquid and dry ingredients in the U S are the teaspoon tablespoon and cup along with halves thirds quarters and eighths of them Pounds ounces fluid ounces and common sizes are also used such as can presumed size varies depending on product jar square e g 1 oz of chocolate stick e g 4 oz butter or fruit vegetable e g a half lemon two medium onions citation needed Temperature EditDegrees Fahrenheit are used in the U S to measure temperatures in most non scientific contexts The Rankine scale of absolute temperature also saw some use in thermodynamics Scientists worldwide use the kelvin and degree Celsius Several U S technical standards are expressed in Fahrenheit temperatures and some American medical practitioners use degrees Fahrenheit for body temperature The relationship between the different temperature scales is linear but the scales have different zero points so conversion is not simply multiplication by a factor Pure water freezes at 32 F 0 C and boils at 212 F 100 C at 1 atm The conversion formula is F 9 5 C 32 displaystyle circ text F tfrac 9 5 circ text C 32 or inversely as C 5 9 F 32 displaystyle circ text C tfrac 5 9 bigl circ text F 32 bigr Other units EditLength 1 hand 4 in 101 6 mm 1 U rack unit 1 75 in 44 45 mm Volume 1 board foot 1 ft 1 ft 1 in 2 360 dm3 Mass 1 slug 1 lbf s2 ft 14 59390 kg Force 1 poundal force to accelerate 1 pound mass 1 foot second second 0 138 Newtons 1 kip 1000 lbf 4 44822 kN Energy 1 foot pound 1 356 J 1 British thermal unit Btu 1 055 kJ Power 1 horsepower 745 7 W 1 ton of refrigeration 12 000 Btu h 3 517 kW Pressure 1 inch of mercury the pressure produced by 25 4 mm depth of mercury 3 376 85 pascals 33 7685 hPa millibars 1 pound per square inch psi 6 895 Pa Torque 1 pound foot 1 356 N m Insulation 1 R value ft2 F h Btu 0 1761 RSI K m2 W Various combination units are in common use these are straightforwardly defined based on the above basic units Sizing systems are used for various items in commerce several of which are U S specific US standard clothing size American wire gauge is used for most metal wire Scoop utensil sizes numbered by scoops per quart Thickness of leather is measured in ounces 1 oz equals 1 64 inch 0 40 mm 22 Bolts and screws follow the Unified Thread Standard rather than the ISO metric screw thread standard Knitting needles in the United States are measured according to a non linear unitless numerical system Aluminum foil is measured in mils 1 1000 inch or 0 0254 mm in the United States Cross sectional area of electrical wire is measured in circular mils in the U S and Canada one circular mil cmil being equal to 5 067 10 4 mm2 or 7 854 10 7 in2 Since this is so small actual wire is commonly measured in thousands of a cmil called either kcmil or MCM The mil or thou is also sometimes used to mean thousandth of an inch Sheet metal in the U S is commonly measured in gauge not to be confused with the American wire gauge which is derived from weight and thus differs by material Nominal Pipe Size is used for the outside diameter of pipes Below NPS14 the NPS number is not consistent with the pipe diameter in inches Copper tubing however is measured in nominal size 1 8 inch less than the outside diameter The Schedule system is used for standard pipe thicknesses Alcohol content is frequently given in proof 2 alcohol by volume The cord is used for volume of firewood The square is used to mean 100 square feet in construction Heat flux in the U S is measured in langleys Other names for U S customary units EditThe United States Code refers to these units as traditional systems of weights and measures 23 Other common ways of referring to the system are customary standard or erroneously English or imperial which refers to the post 1824 reform measures used throughout the British Empire amp Commonwealth countries Another term is the foot pound second FPS system as opposed to centimeter gram second CGS and meter kilogram second MKS systems Tools and fasteners with sizes measured in inches are sometimes called SAE bolts or SAE wrenches to differentiate them from their metric counterparts The Society of Automotive Engineers SAE originally developed fasteners standards using U S units for the U S auto industry the organization now uses metric units 24 See also EditBoard foot Conversion of units History of measurement and units of measurement Plan for Establishing Uniformity in the Coinage Weights and Measures of the United States 1790 Mars Climate Orbiter which failed due to a measurement units related software bug Standard cubic footReferences Edit Barbrow L E and Judson L V 1976 Weights and Measures of the United States National Bureau of Standards Special Publication 447 p 5 6 T C Mendenhall Superintendent of Standard Weights and Measures Order of April 5 1893 Archived September 30 2012 at the Wayback Machine published as Appendix 6 to the Report for 1893 of the Coast and Geodetic Survey a b c Astin A V Karo H A and Mueller F H June 25 1959 Doc 59 5442 Refinement of Values for the Yard and the Pound Federal Register Note that 999 998 3937 254 Laws and Metric Program U S National Institute of Standards and Technology 2010 English units of measurement The Columbia Encyclopedia 6th ed 2001 2007 archived copy Martin Gardner May 4 2012 Fads and Fallacies in the Name of Science Courier Corporation pp 180 ISBN 978 0 486 13162 7 a b References Weights and Measures The World Factbook Washington D C Central Intelligence Agency Retrieved April 22 2021 Robyn Williams February 8 1998 Trouble with the Metric System Australian Radio National Ockham s Razor Ed Tenner May 2005 The Trouble with the Meter Technologyreview com a b c d e Roberts R W February 3 1975 Federal Register republished in Barbrow L E and Judson L V 1976 Weights and Measures of the United States National Bureau of Standards Special Publication 447 p 36 Barton John W Bowers Shelby L Butcher Tina G Harshman Richard A Lee G Diane amp Warfield Lisa eds Specifications Tolerances and Other Technical Requirements for Weighing and Measuring Devices 2022 Edition n p National Institute of Standards and Technology pages B 7 C 20 a b c Frequently Asked Questions about the National Geodetic Survey National Geodetic Survey Retrieved May 16 2009 Astin A V July 27 1968 Federal Register Archived October 5 2006 at the Wayback Machine Republished in Barbrow L E and Judson L V Weights and Measures of the United States A Brief History National Bureau of Standards Special Publication 447 pp 34 35 National Institute of Standards and Technology 2008 Guide for the Use of the International System of Units SI The recommended symbol for the liter in the United States is L per National Institute of Standards and Technology 1995 Guide for the Use of the International System of Units SI Special Publication 811 a b 101st Conference on Weights and Measures 2016 2017 Specifications Tolerances and Other Technical Requirements for Weighing and Measuring Devices National Institute of Standards and Technology p C 6 C 11 C 16 Summary of State Laws and Regulations in Weights and Measures Archived December 5 2011 at the Wayback Machine 2005 National Institute of Standards and Technology NIST Handbook 44 Appendix C General Tables of Units of Measurement page C 6 Avoirdupois Units of Mass Archived October 18 2011 at the Wayback Machine United States Department of Agriculture United States Department of Agriculture August 20 2019 Retrieved May 28 2020 Weights and Measures of agricultural commodities PDF United States Department of Agriculture National Agricultural Statistics Service Retrieved May 28 2020 Title 21 101 9 Nutrition labeling of food PDF Code of Federal Regulations US Government Printing Office April 12 2012 Retrieved November 2 2014 For nutrition labeling purposes a teaspoon means 5 milliliters mL a tablespoon means 15 mL a cup means 240 mL 1 fl oz means 30 mL and 1 oz in weight means 28 g Wells Larry J 1981 Makin Leather A Manual of Primitive and Modern Leather Skills Cedar Fort p 13 ISBN 0882908359 15 U S C 205b Rules for SAE Use of SI Metric Units PDF Society of Automotive Engineers Inc May 1999 Retrieved July 1 2012 External links EditRowlett s Dictionary of Units of Measurement archived Retrieved from https en wikipedia org w index php title United States customary units amp oldid 1092282799, wikipedia, wiki, book,

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