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Encyclopedia > U.S. customary units

U.S. customary units, commonly known in the United States as English units or standard units, are units of measurement that are currently used in the U.S., in some cases alongside units from SI (the International System of Units—the modern metric system). The U.S. system of units is similar to the Imperial system which was used officially in the U.K. until 1995 (and which still has wide unofficial usage there). Both systems derive from the evolution of local units over the centuries, as a result of standardization efforts in England; the local units themselves mostly trace back to Roman and Anglo-Saxon units. Today, U.S. customary units are defined in terms of SI units. The Imperial units are an irregularly standardized system of units that have been used in the United Kingdom and its former colonies, including the Commonwealth countries. ... The word unit means any of several things: Unit of measurement or physical unit, a fundamental quantity of measurement in science or engineering. ... The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ... The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... The Imperial units are an irregularly standardized system of units that have been used in the United Kingdom and its former colonies, including the Commonwealth countries. ... For an explanation of terms like England, (Great) Britain and United Kingdom see British Isles (terminology) Motto: Dieu et mon droit (Royal motto) (French for God and my right)3 Anthem: God Save the Queen4 Capital London Largest city London Official language(s) English de facto 5 Government Monarch Prime... Wikimedia Commons has media related to: England Travel guide to England from Wikitravel English language English law English (people) List of monarchs of England – Kings of England family tree List of English people Angeln (region in northern Germany, presumably the origin of the Angles for whom England is named) UK...


In the Omnibus Trade and Competitiveness Act of 1988, the United States government designated the metric system of measurement as "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, especially small business, as it voluntarily converts to the metric system of measurement. This process of legislation and conversion is known as metrication, and in the U.S. is most evident in labeling requirements on food products, where SI units are almost always presented alongside customary units. Speedometer gauges on a car showing the speed of the vehicle in miles and kilometres per hour. ...


However, metrication in the United States has been less forcefully imposed than in other countries, and has encountered more resistance from industrial and consumer market forces, so customary units are still widely used on consumer products and in industrial manufacturing; only in military, medical and scientific contexts are SI units generally the norm. Since everyday weights and measures are mostly non-SI, children in U.S. public schools are generally taught customary units before SI, although many schools are now attempting to teach SI units at an earlier age. The history and current usage of the metric system in the United States has been rocky and unsteady. ...


Other countries had (or still have, unofficially), customary units of their own, sometimes very similar in name and measure to the U.S. customary units, since they often shared the same Germanic or Roman origins. Frequently, however, these units designated quite different sizes. For example, in different countries, the mile ranged from 1 to 10 kilometers, and even foot and pound had varying definitions. Even within the U.S., at least through the 19th century, the customary units of measure were sometimes just as variable. Eventually, most countries, including the U.S., redefined their customary units in terms of SI units like kilogram and meter. Often, though, unlike English units, they were rounded to "nice" SI values, leading to their use in colloquial speech, alongside SI terms, into the present day. A mile is a unit of distance (or, in physics terminology, length) currently defined as 5,280 feet, 1,760 yards, or 63,360 inches. ... A foot (plural: feet) is a non-SI unit of distance or length, measuring around a third of a metre. ... Officially the pound is the name for at least three different units of mass: The pound (avoirdupois). ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ... The metre, or meter (symbol: m) is the SI base unit of length. ...


Historically, a wide range of non-SI units have been used in the United States. and United Kingdom, and in England before that, but many of these have fallen into disuse. This article only deals with the units commonly used or officially defined in the United States.

Contents


Units of length

The system for measuring length in the United States' customary system is based on the inch, foot, yard, and mile. However, for each of these units there exist two slightly different definitions, yielding two different systems of measure - international measure, and U.S. survey measure. The relationships between the different units within each measure is the same, but each measure has a slightly different definition in terms of metric units. Mid-19th century tool for converting between different standards of the inch An inch is an Imperial and U.S. customary unit of length. ... A foot (plural: feet) is a non-SI unit of distance or length, measuring around a third of a metre. ... This article is about the unit of measure known as the yard. ... A mile is a unit of distance (or, in physics terminology, length) currently defined as 5,280 feet, 1,760 yards, or 63,360 inches. ...


One inch international measure is exactly 25.4 millimeters, while one inch U.S. survey measure is defined so that 39.37 inches is exactly 1 meter. For most applications, the difference is insignificant (about 3 millimeter per mile). International measure is used for everyday use, engineering, and commerce in the United States, while survey measure is used only for surveying. Mid-19th century tool for converting between different standards of the inch An inch is an Imperial and U.S. customary unit of length. ... The metre, or meter (symbol: m) is the SI base unit of length. ...


International measure, agreed in 1959, uses the same definition of the units involved as is used in the UK and other Commonwealth countries. Before that date, those other countries still used separate standards. U.S. survey measure uses an older definition of the units (specified by the former National Bureau of Standards in 1893) which the United States used prior to adopting international measure. Previous to this agreement, the US standard was identical to survey measure. 1959 (MCMLIX) was a common year starting on Thursday of the Gregorian calendar. ... As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... 1893 was a common year starting on Sunday (see link for calendar). ...

  • 1 inch (in) = 25.4 mm
  • 1 foot (ft) = 12 in = 30.48 cm
  • 1 yard (yd) = 3 ft = 91.44 cm
  • 1 mile (mi) = 5280 ft = 1760 yd = 1.609344 km
  • 1 rod (unit) (rd) (also called pole or perch) = 16.5 ft = 5.0292 m
  • 1 furlong (fur) = 40 rd = 660 ft = 201.168 m
  • 1 mile (survey) = 8 fur = 5280 ft ≈ 1.609347 km

Sometimes, for surveying purposes, units known as Gunther's Chain Measure (or equivalently Surveyor's Chain Measure) are used. These units are defined by survey feet as follows: Mid-19th century tool for converting between different standards of the inch An inch is an Imperial and U.S. customary unit of length. ... A foot (plural: feet) is a non-SI unit of distance or length, measuring around a third of a metre. ... This article is about the unit of measure known as the yard. ... A mile is a unit of distance (or, in physics terminology, length) currently defined as 5,280 feet, 1,760 yards, or 63,360 inches. ... A rod is a unit of length, equal to 5. ... The 5 furlong (1006 m) post on Epsom Downs A furlong is a measure of distance within Imperial units and U.S. customary units. ... A mile is a unit of distance (or, in physics terminology, length) currently defined as 5,280 feet, 1,760 yards, or 63,360 inches. ...

  • 1 link (li) = 7.92 in = 0.66 ft = 0.001 fur (approx. 201.168 mm)
  • 1 chain (ch) (Gunter's) = 100 li = 66 ft (approx. 20.1168 m)

To measure depths at sea, fathoms are used: The term link can refer to: // Computer-related A connection between two components of a network. ... Look up chain in Wiktionary, the free dictionary. ...

A fathom is a non-SI unit of length. ... A cable length is a nautical unit of measure, for which at least four definitions seem to exist: Common definition: 1/10 nautical mile, i. ... The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ...

Units of area

The units of area in the U.S. customary system are mostly based on the units of length squared, e.g., square inch (sq in, 645.16 mm²). Since the U.S. customary system has two differing definitions of the foot (international and survey), there are also two differing definitions for the square foot. A square inch is by definition the area enclosed by a square with sides each 1 inch long. ...

  • 1 square foot (sq ft) = 144 sq in = 929.0304 cm²
  • 1 square rod (sq rd) = 272.25 sq ft = 25.29285264 m²
  • 1 acre = 10 sq ch = 1 fur × 1 ch = 160 sq rd = 43,560 sq ft = 4046.8564224 m²
  • 1 square mile (sq mi) = 27,878,400 sq ft = 3,097,600 sq yd = 640 acres = 2.589988110336 km²

The Public Land Survey System, used to divide land in most of the United States, uses the survey mile to divide land into regular square parcels, such "sections" and "townships." However, these terms aren't used for general area measurement, instead used to indicate particular parcels of land in a rectangular grid. A square foot is by definition the area enclosed by a square with sides each 1 foot long. ... An acre is an English unit of area. ... A square mile is the area equal to a square with sides each 1 mile long. ... This General Land Office map shows the theoretical sectioning of a standard survey township. ...


Units of capacity and volume

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. A cubic inch is the volume of a cube which is one inch long on each edge. ... The cubic foot (symbols ft³, cu. ... The cubic yard (symbols yd³, cu. ...


Other than the cubic foot, cubic inch 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. This article is about post-1824 Imperial units, please see also English unit, U.S. customary unit or Avoirdupois. ...


Technically speaking, since these units are defined in terms of the inch, it would make a difference whether international or survey measure was used. However, in practice, the difference between the two definitions would be imperceptible, and in any case in defining volumes international measure is used.


Volume in general

  • 1 cubic inch (in³ or cu in) = 16.387,064 mL (or cm³)
  • 1 cubic foot (ft³ or cu ft) = 1728 cu in ≈ 28.317 L
  • 1 cubic yard (yd³ or cu yd) = 27 cu ft ≈ 7.646 hL
  • 1 cord = 128 cu ft ≈ 3.624,556 m³
  • 1 acre-foot = 43,560 cu ft ≈ 325,851 gallons ≈ 12,334.818 m³

A cubic inch is the volume of a cube which is one inch long on each edge. ... A cubic centimetre (cm3) is an SI derived unit of volume, equal to the volume of a cube with side length of 1 centi metre. ... The cubic foot (symbols ft³, cu. ... The litre (spelled litre in Commonwealth English and liter in American English) is a unit of capacity. ... The cubic yard (symbols yd³, cu. ... Wood burning is the largest current use of biomass derived energy. ... An acre foot is a unit of volume commonly used in the United States in reference to large-scale water resources, such as reservoirs, aqueducts, canals, and river flows. ...

Liquid volume

  • 1 minim (min) = 1/480 fl oz ≈ 61.612 µL
  • 1 fluid dram (fl dr) = 1/8 fl oz = 60 min ≈ 3.697 mL
  • 1 fluid ounce (fl oz) = 1/128 gal = 8 fl dr ≈ 29.574 mL
  • 1 gill (gi) = 7.21875 cu in = 4 fl oz ≈ 118.294 mL
  • 1 cup = 2 gi = 8 fl oz ≈ 236.588 mL
  • 1 pint (pt) = 2 cups = 4 gi = 16 fl oz ≈ 473.176 mL
  • 1 fifth = 25.6 fl oz ≈ 757.082 mL
  • 1 quart (qt) = 2 pt = 32 fl oz ≈ 946.353 mL
  • 1 gallon (gal) = 231 cu in = 4 qt = 128 fl oz = 3.785411784 L

The gill—pronounced /dʒɪl/—is basically a paper unit which is never actually used in the United States. Distilled liquor and wine were bottled in fifths until 1973; when the term "fifth" is used now it almost always means 750 mL. "Fifth" refers to the fact that the measure is equal to one fifth of a gallon. A fluid ounce is a unit of volume in both the Imperial system of units and the U.S. customary units system. ... The gill is a unit of measurement for volume, equal in the USA to one half of a cup (120 ml). ... The cup is a unit of measurement for volume, used in cooking recipes in several countries. ... The pint is a unit of volume. ... Fifth means one part out of five (1/5, 0. ... A quart is a unit of measurement for volume. ... The gallon (abbr. ... 1973 (MCMLXXIII) was a common year starting on Monday. ...


Dry volume

  • 1 pint (pt) ≈ 550.610 mL
  • 1 quart (qt) = 2 pt ≈ 1.101 L
  • 1 gallon (gal) = 4 qt = 268.8025 in³ = 4.404 842 803 2 L
  • 1 peck (pk) = 8 qt = 2 gal ≈ 8.81 L
  • 1 bushel (bu) = 2150.42 cu in = 4 pk ≈ 35.239 L

A quart is a unit of measurement for volume. ... The gallon (abbr. ... A peck is an Imperial unit and U.S. customary unit of dry volume, equivalent in each of these systems to 8 dry quarts, or 16 dry pints. ... A bushel is a unit of volume, used (with somewhat different definitions) in the systems of Imperial units and U.S. customary units. ...

Units of mass

There have historically been four different English systems of mass: Tower weight, Troy weight, Avoirdupois system, and Apothecaries' system. Tower weight fell out of use (due to legal prohibition) centuries ago, and was never used in the United States. Troy weight is still used to weigh precious metals. Apothecaries weight, once used in pharmacy, has been largely replaced by metric measurements. Avoirdupois weight is the primary system of mass in the U.S. customary system. A Tower pound was a unit of weight equal to 5400 grains (just over 3/4 of an ordinary (avoirdupois) pound). ... Troy weight is a system of units of mass customarily used for precious metals and gemstones. ... The avoirdupois system is a system of weights defining terms such as pound and ounce. ... The apothecaries system of mass is an obsolete system formerly used by apothecaries (now called pharmacists or chemists) in English-speaking countries. ...


The Avoirdupois units are legally defined as measures of mass, but the names of these units are sometimes applied to measures of force. For instance, in most contexts, the pound avoirdupois is used as a unit of mass, but in the realm of physics, the term "pound" can represent "pound-force" (a unit of force properly abbreviated as "lbf"). Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... In physics, a net force acting on a body causes that body to accelerate; that is, to change its velocity. ... Officially the pound is the name for at least three different units of mass: The pound (avoirdupois). ... The pound-force is a non-SI unit of force or weight (properly abbreviated lbf or lbf). The pound-force is equal to a mass of one pound multiplied by the standard acceleration due to gravity on Earth (which is defined as exactly 9. ...


Troy weight, avoirdupois weight, and apothecaries weight are all defined in terms of 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 apothecaries 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). The dram was once known as the drachm. Dram can mean several things: for the imperial unit of volume see dram (volume) for the imperial unit of weight or mass see avoirdupois and apothecaries system of mass for the Armenian monetary unit see dram (currency) DRAM is a type of RAM and unlike dram is spelled in all... Dram can mean several things: for the imperial unit of volume see dram (volume) for the imperial unit of weight or mass see avoirdupois and apothecaries system of mass for the Armenian monetary unit see dram (currency) DRAM is a type of RAM and unlike dram is spelled in all... Dram can mean several things: for the imperial unit of volume see dram (volume) for the imperial unit of weight or mass see avoirdupois and apothecaries system of mass for the Armenian monetary unit see dram (currency) DRAM is a type of RAM and unlike dram is spelled in all...


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 ounce avoirdupois.


The pound avoirdupois, which forms the basis of the U.S. customary system of mass, is defined as exactly 453.59237 grams. All the other units of mass are defined in terms of it. The gram or gramme, symbol g, is a unit of mass. ...


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 British Imperial system is identical to that in the U.S. customary system.


Avoirdupois weight

See Avoirdupois. The avoirdupois system is a system of weights defining terms such as pound and ounce. ...

  • 1 grain (gr) = 64.79891 mg
  • 1 dram (dr) = 27 11/32 gr = 1/16 oz ≈ 1.772 g
  • 1 ounce (oz) = 16 dr = 437.5 gr ≈ 28.35 g
  • 1 pound (lb) = 16 oz = 7000 gr = 453.59237 g
  • 1 hundredweight (cwt) = 100 lb = 45.359237 kg
  • 1 ton (t) = 20 cwt = 2000 lb = 907.18474 kg ≈ 0.907 t

The ton and hundredweight above are referred to as the short ton, and the short hundredweight, to distinguish them from the British Imperial ton and hundredweight, which are larger and hence are referred to as the long ton and long hundredweight. The long ton has limited use in the United States. A grain is a unit of mass equal to 0. ... The milligram (symbol mg) is an SI unit of mass. ... Dram can mean several things: for the imperial unit of volume see dram (volume) for the imperial unit of weight or mass see avoirdupois and apothecaries system of mass for the Armenian monetary unit see dram (currency) DRAM is a type of RAM and unlike dram is spelled in all... The ounce is the name for a number of different units of mass (oz), and also of two units of fluid volume (fl oz) and of one unit of force, the ounce-force (ozf). ... Officially the pound is the name for at least three different units of mass: The pound (avoirdupois). ... Hundred weight or hundredweight is a unit of measurement for mass in both the system of measurement used in the United Kingdom and Ireland (and previously throughout the British Commonwealth), and in the system used in the United States. ... The word ton or tonne is derived from the Old English tunne, and ultimately from the Old French tonne, and referred originally to a large cask with a capacity of 252 wine gallons, which holds approximately 2100 pounds of water. ...

  • 1 long hundredweight = 112 lb ≈ 50.802 kg
  • 1 long ton = 20 long cwt = 2240 lb ≈ 1016.047 kg ≈ 1.016 t

A long ton is the name used in the US for the unit called the ton in the avoirdupois or Imperial system of measurements, as used (alongside the metric system) in the United Kingdom and to some extent in other Commonwealth countries. ...

Apothecaries' weight

See Apothecaries' system of mass. The apothecaries system of mass is an obsolete system formerly used by apothecaries (now called pharmacists or chemists) in English-speaking countries. ...


The grain has the same definition as for avoirdupois weight.

  • 1 scruple (s ap) = 20 gr ≈ 1.296 g
  • 1 dram apothecaries (dr ap) = 3 s ap ≈ 3.888 g
  • 1 ounce apothecaries (oz ap) = 1 oz t = 8 dr ap = 480 gr ≈ 31.103 g
  • 1 pound apothecaries (lb ap) = 1 lb t = 12 oz ap = 5760 gr ≈ 373.242 g

The pound and ounce apothecaries are identical to the pound and ounce troy.


Troy weight

The grain has the same definition as for Avoirdupois weight.

  • 1 pennyweight (dwt) = 24 gr ≈ 1.555 g
  • 1 ounce troy (oz t) = 20 dwt = 480 gr ≈ 31.103 g
  • 1 pound troy (lb t) = 12 oz t = 5760 gr ≈ 373.242 g

A pennyweight (symbol dwt) is an obsolete unit of mass which is the same as 24 grains, 1/240th of a troy pound, 1/20th of a troy ounce, or approximately 1. ...

Cooking measures

The most common cooking weights and measures in the U.S. are as follows:

  • 1 teaspoon = 1/3 tbsp = 1/6 fl oz ≈ 5 mL
  • 1 tablespoon (tbsp) = 1/2 fl oz = 4 fl dr ≈ 15 mL
  • 1 cup = 8 fl oz ≈ 240 mL
  • 1 stick (of butter) = 1/4 lb = 4 oz ≈ 115 g

See Cooking weights and measures for more details. Teaspoon and sugar A teaspoon is a small spoon that can hold about 5 milliliters of liquid. ... This tablespoon has a capacity of about 1 tbsp. ... The cup is a unit of measurement for volume, used in cooking recipes in several countries. ... // United States measures Note that the measurements in this section are in U.S. customary units. ...


Grain measures

These are derived from the volume measures and there have been more for other crops.

  • 1 bushel (maize) = 56 lb ≈ 25.401 kg
  • 1 bushel (wheat) = 60 lb ≈ 27.216 kg

A bushel is a unit of volume, used (with somewhat different definitions) in the systems of Imperial units and U.S. customary units. ...

Units of temperature

Traditionally, degrees Fahrenheit are used in the United States to measure temperatures. Fahrenheit is a temperature scale named after the German physicist Gabriel Fahrenheit (1686–1736), who proposed it in 1724. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ...

  • Pure water freezes at 32 °F and boils at 212 °F at 1 atm.
  • Water saturated with common salt freezes at -6.02 °F.
  • Conversion formula: F=frac{9}{5}C+32

When expressed as a measurement, an atmosphere (symbol: atm) or standard atmosphere is a unit of pressure roughly equal to the average atmospheric pressure at sea level on Earth. ...

Other units

The British thermal unit (BTU or Btu) is a unit of energy still used in the United States. ... The horsepower (hp) is the name of several non-metric units of power. ... A hand (or handbreadth) is a unit of length measurement, usually based on the breadth of a male human hand and thus around 1 dm, i. ... A calorie is a unit of measurement for energy. ... Rankine is a now rarely used temperature scale named after the Scottish engineer and physicist William John Macquorn Rankine, who proposed it in 1859. ... The board-foot is a specialized unit of volume for measuring lumber in the United States and Canada. ... The R-value is the measure of thermal resistance. ...

See also

// Introduction Units of measurement were among the earliest tools invented by humans. ... // The metric system Metric systems of units have evolved since the adoption of the first well-defined system in France in 1791. ... // Introduction The definition, agreement and practical use of units of measurement have played a crucial role in human endeavour from early ages up to this day. ... The term English units refers to one of a number of systems of units of measurement, some obsolete, and some still in use. ... This article is about post-1824 Imperial units, please see also English unit, U.S. customary unit or Avoirdupois. ... Both the Imperial and U.S. customary derive from earlier English systems. ... This article lists conversion factors between a number of units of measurement. ... Informal conversion of common measuring units often needs to be done without calculator or computer. ... A metrified Imperial system is a proposal for a metrication and unification of the English systems of measures. ... Speedometer gauges on a car showing the speed of the vehicle in miles and kilometres per hour. ... The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ...

External links

  • Source: Appendix C, NIST Handbook 44, 2002 edition.
  • Judson, Lewis B., Weights and Measures Standards of the United States: A brief history, NBS Special Publication 447, orig. iss. October 1963, updated March 1976 (46 page PDF file).
  • Jacques J. Proot's Anglo-Saxon weights & measures page.

 
 

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