United States customary units - AbsoluteAstronomy.com

United States customary units are a system of measurements

Units of measurement

A unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention and/or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of...

commonly used in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. Many U.S. units are virtually identical to their imperial counterparts, but the U.S. customary system developed from English unit

English unit

English units are the historical units of measurement used in England up to 1824, which evolved as a combination of the Anglo-Saxon and Roman systems of units...

s used in the British Empire

British Empire

The British Empire comprised the dominions, colonies, protectorates, mandates and other territories ruled or administered by the United Kingdom. It originated with the overseas colonies and trading posts established by England in the late 16th and early 17th centuries. At its height, it was the...

before the system of imperial units was standardized in 1824. Several numerical differences from the imperial system are present.

The vast majority of U.S. customary units have been defined in terms of the metre

Metre

The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...

and the kilogram

Kilogram

The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

since the Mendenhall Order

Mendenhall Order

The Mendenhall Order marked a decision to change the fundamental standards of length and mass of the United States from the customary standards based on those of England to metric standards. It was issued on April 5, 1893 by Thomas Corwin Mendenhall, superintendent of the U.S...

of 1893 (and, in practice, for many years before that date). These definitions were refined in 1959.

The U.S. is the only industrialized nation that does not mainly use the metric system

Metric system

The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...

in its commercial and standards activities, although the International System of Units

International System of Units

The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

(SI, often referred to as "metric") is commonly used in both the US Armed Forces and in fields relating to science

Science

Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...

, and increasingly in medicine, aviation, government as well as various sectors of industry.

History

The U.S. system of units is similar to the British imperial system. Both systems derive from the evolution of local units over the centuries, as a result of standardization efforts in the United Kingdom; the local units themselves mostly trace back to Roman and Anglo-Saxon units. Today, these units are defined in terms of SI units.

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

Metrication

Metrication refers to the introduction and use of the SI metric system, the international standard for physical measurements. This has involved a long process of independent and systematic conversions of countries from various local systems of weights and measures. Metrication began in France in...

, and in the U.S. is most evident in labeling requirements on food products, where SI units are almost always presented alongside customary units.

However, metrication in the United States

Metrication in the United States

Metrication is the process of introducing the International System of Units , a metric system of measurement, to replace the historical or customary units of measurement of a country or region...

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.

The customary system was championed by the United States-based International Institute for Preserving and Perfecting Weights and Measures in the late 19th century. Advocates of the customary system saw the French Revolutionary, or metric, system as atheistic. An auxiliary of the Institute in Ohio published a poem reading:

Then down with every "metric" scheme

Taught by the foreign school,

We'll worship still our Father's God!

And keep our Father's "rule"!

A perfect inch, a perfect pint,

The Anglo's honest pound,

Shall hold their place upon the earth,

Till time's last trump shall sound!

One adherent of the customary system called it "a just weight and a just measure, which alone are acceptable to the Lord."

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 inch measurements are more suitable when distances are frequently divided by two.

Other countries had (or still have, unofficially) customary units of their own, sometimes very similar in name and measure to U.S. customary units, since they often share the same Germanic or Roman origins. Frequently, however, these units designate quite different sizes. For example, the mile
Mile
A mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...

ranged by country from one half to five U.S. miles; even foot and pound

Pound (mass)

The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...

had varying definitions. Until the twentieth century the customary units of measure in the United States were sometimes just as variable. Historically, a wide range of non-SI units were used in the United States and in Britain, but many have fallen into disuse. This article deals only with the units commonly used or officially defined in the United States.

Units of length

Unit	Divisions	SI Equivalent
Exact relationships shown in boldface
International
1 point Point (typography) In typography, a point is the smallest unit of measure, being a subdivision of the larger pica. It is commonly abbreviated as pt. The point has long been the usual unit for measuring font size and leading and other minute items on a printed page.... (p)		352.8 µm
1 pica (P̸)	12 p	4.233 mm
1 inch Inch An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot... (in)	6 P̸	2.54 cm
1 foot (ft)	12 in
1 yard Yard A yard is a unit of length in several different systems including English units, Imperial units and United States customary units. It is equal to 3 feet or 36 inches... (yd)	3 ft
1 mile Mile A mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile... (mi)
Survey
1 link (li)	ft or 7.92 in
1 (survey) foot (ft)	m
1 rod Rod (unit) The rod is a unit of length equal to 5.5 yards, 5.0292 metres, 16.5 feet, or of a statute mile. A rod is the same length as a perch or a pole. In old English, the term lug is also used.-History:... (rd)	25 li or 16.5 ft
1 chain Chain (unit) A chain is a unit of length; it measures 66 feet or 22 yards or 100 links . There are 10 chains in a furlong, and 80 chains in one statute mile. An acre is the area of 10 square chains... (ch)	4 rd
1 furlong Furlong A furlong is a measure of distance in imperial units and U.S. customary units equal to one-eighth of a mile, equivalent to 220 yards, 660 feet, 40 rods, or 10 chains. The exact value of the furlong varies slightly among English-speaking countries.... (fur)	10 ch
1 survey (or statute) mile Mile A mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile... (mi)	8 fur
1 league League (unit) A league is a unit of length . It was long common in Europe and Latin America, but it is no longer an official unit in any nation. The league originally referred to the distance a person or a horse could walk in an hour... (lea)	3 mi
Nautical
1 fathom Fathom A fathom is a unit of length in the imperial and the U.S. customary systems, used especially for measuring the depth of water.There are 2 yards in an imperial or U.S. fathom... (ftm)	2 yd
1 cable (cb)	120 ftm or 1.091 fur
1 nautical mile Nautical mile The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator... (NM or nmi)	8.439 cb or 1.151 mi	1.852 km

The system for measuring length in the United States customary system is based on the inch

Inch

An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...

, foot, yard

Yard

A yard is a unit of length in several different systems including English units, Imperial units and United States customary units. It is equal to 3 feet or 36 inches...

, and mile

Mile

A mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical 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 metres except for some applications in surveying. This definition was agreed with the UK

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

and other Commonwealth

Commonwealth of Nations

The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-four independent member states...

countries, and so is often termed international measure.

When international measure was introduced in the English-speaking countries, the basic geodetic datum in North America was the North American Datum

North American Datum

The North American Datum is the official datum used for the primary geodetic network in North America.In the fields of cartography and land-use there are currently two North American Datums in use: the North American Datum of 1927 and the North American Datum of 1983...

of 1927 (NAD27), which had been constructed by triangulation

Triangulation

In trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly...

based on the definition of the foot in the Mendenhall Order

Mendenhall Order

of 1893, that is 1 foot = meters: this definition was retained for data derived from NAD27, but renamed the U.S. 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 U.S. survey foot, for a difference of about inch (3 mm) per mile — but it affects the definition of the State Plane Coordinate System

State Plane Coordinate System

The State Plane Coordinate System is a set of 124 geographic zones or coordinate systems designed for specific regions of the United States. Each state contains one or more state plane zones, the boundaries of which usually follow county lines...

s (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 U.S. survey feet and an eighth state in international feet: the other 42 states use only meter-based SPCSs.

State legislation is also important for determining 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 U.S. 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.

Units of area

Unit	Divisions	SI Equivalent
Exact relationships shown in boldface
1 square survey foot (sq ft or ft²)	144 square inches	m²
1 square chain (sq ch) or (ch²)	feet² (survey) or 16 sq rods	m²
1 acre Acre The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and, in the United States, the survey acre. The most common use of the acre is to measure tracts of land.The acre is related...	sq ft (survey) or 10 sq ch	m²
1 section	640 acres or 1 sq mi (survey)	km²
1 survey township Survey township Survey township, sometimes called Congressional township, as used by the United States Public Land Survey System, refers to a square unit of land, that is nominally six miles on a side... (twp)	36 sections or 4 sq leagues	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).

Units of capacity and volume

Volume in general
Unit	Divisions	SI Equivalent
1 cubic inch Cubic inch The cubic inch is a unit of measurement for volume in the Imperial units and United States customary units systems. It is the volume of a cube with each of its 3 sides being one inch long.... (cu in) or (in³)
1 cubic foot Cubic foot The cubic foot is an Imperial and US customary unit of volume, used in the United States and the United Kingdom. It is defined as the volume of a cube with sides of one foot in length.-Conversions:- Symbols :... (cu ft) or (ft³)
1 cubic yard Cubic yard A cubic yard is an Imperial / U.S. customary unit of volume, used in the United States, Canada, and the UK. It is defined as the volume of a cube with sides of 1 yard in length.-Symbols:... (cu yd) or (yd³)	27 cu ft
1 acre-foot (acre ft)

The cubic inch

Cubic inch

The cubic inch is a unit of measurement for volume in the Imperial units and United States customary units systems. It is the volume of a cube with each of its 3 sides being one inch long....

, cubic foot

Cubic foot

The cubic foot is an Imperial and US customary unit of volume, used in the United States and the United Kingdom. It is defined as the volume of a cube with sides of one foot in length.-Conversions:- Symbols :...

and cubic yard

Cubic yard

A cubic yard is an Imperial / U.S. customary unit of volume, used in the United States, Canada, and the UK. It is defined as the volume of a cube with sides of 1 yard in length.-Symbols:...

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 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.

Fluid volume

Liquid volume
Most common measures shown in italic font Exact conversions in bold font
Unit	Divisions	SI Equivalent
1 minim Minim (unit) The minim is a unit of volume in both the imperial and US customary systems of measurement. Specifically it is of a fluidram or of a fluid ounce.... (min)	~ 1 drop or 0.95 grain of water
1 US fluid dram (fl dr)	60 min
1 teaspoon Teaspoon A teaspoon, an item of cutlery, is a small spoon, commonly part of a silverware place setting, suitable for stirring and sipping the contents of a cup of tea or coffee... (tsp)	80 min
1 tablespoon Tablespoon A tablespoon is a type of large spoon usually used for serving. A tablespoonful, the capacity of one tablespoon, is commonly used as a measure of volume in cooking... (Tbsp)	3 tsp or 4 fl dr
1 US fluid ounce Fluid ounce A fluid ounce is a unit of volume equal to about 28.4 mL in the imperial system or about 29.6 mL in the US system. The fluid ounce is distinct from the ounce, which measures mass... (fl oz)	2 Tbsp or 1.041 oz av of water
1 jigger (jig)	3 Tbsp
1 US gill Gill (unit) The gill is a unit of measurement for volume equal to a quarter of a pint. It is no longer in common use, except in regard to the volume of alcoholic spirits measures but it is also kept alive by the occasional reference, such as in the cumulative song, "The Barley Mow".Imperial gillUnited States... (gi)	4 fl oz
1 US cup Cup (unit) The cup is a customary unit of measurement for volume, used in cooking to measure liquids and bulk foods such as granulated sugar... (cp)	2 gi or 8 fl oz
1 (liquid) US pint Pint The pint is a unit of volume or capacity that was once used across much of Europe with values varying from state to state from less than half a litre to over one litre. Within continental Europe, the pint was replaced with the metric system during the nineteenth century... (pt)	2 cp or 16.65 oz av of water
1 (liquid) US quart Quart The quart is a unit of volume equal to a quarter of a gallon, two pints, or four cups. Since gallons of various sizes have historically been in use, quarts of various sizes have also existed; see gallon for further discussion. Three of these kinds of quarts remain in current use, all approximately... (qt)	2 pt
1 (liquid) US gallon Gallon The gallon is a measure of volume. Historically it has had many different definitions, but there are three definitions in current use: the imperial gallon which is used in the United Kingdom and semi-officially within Canada, the United States liquid gallon and the lesser used United States dry... (gal)	4 qt or 231 cu in
1 (liquid) barrel Barrel (unit) A barrel is one of several units of volume, with dry barrels, fluid barrels , oil barrel, etc... (bbl)	31.5 gal or hogshead
1 oil barrel (bbl)	42 gal or hogshead
1 hogshead Hogshead A hogshead is a large cask of liquid . More specifically, it refers to a specified volume, measured in either Imperial units or U.S. customary units, primarily applied to alcoholic beverages such as wine, ale, or cider....	63 gal or or 524.7 lb of water

One fluid ounce is of a U.S. pint, of a U.S. quart, and of a U.S. gallon. The fluid ounce derives its name originally from being the volume of one ounce avoirdupois

Avoirdupois

The avoirdupois system is a system of weights based on a pound of 16 ounces. It is the everyday system of weight used in the United States and is still widely used to varying degrees by many people in Canada, the United Kingdom, and some other former British colonies despite the official adoption...

of water, but in the U.S. it is defined as of a U.S. 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.
There are varying standards for barrel

Barrel (unit)

A barrel is one of several units of volume, with dry barrels, fluid barrels , oil barrel, etc...

for some specific commodities, including 31 gal for beer, 40 gal for whiskey or kerosene, and 42 gal for petroleum. The general standard for liquids is 31.5 gal or half a hogshead. The common 55 gallon size of drum

Drum (container)

A drum is a cylindrical container used for shipping bulk cargo. Drums can be made of steel, dense paperboard , or plastics, and are generally used for the transportation and storage of liquids and powders. Drums are often certified for shipment of dangerous goods...

for storing and transporting various products and wastes is sometimes confused with a barrel, though it is not a standard measure.

In the United States, 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 and gill are rarely used currently.

Dry volume

Dry volume
Unit	Divisions	SI Equivalent
1 (dry) pint Pint The pint is a unit of volume or capacity that was once used across much of Europe with values varying from state to state from less than half a litre to over one litre. Within continental Europe, the pint was replaced with the metric system during the nineteenth century... (pt)	33.60 cu in
1 (dry) quart Quart The quart is a unit of volume equal to a quarter of a gallon, two pints, or four cups. Since gallons of various sizes have historically been in use, quarts of various sizes have also existed; see gallon for further discussion. Three of these kinds of quarts remain in current use, all approximately... (qt)	2 pt
1 (dry) gallon Gallon The gallon is a measure of volume. Historically it has had many different definitions, but there are three definitions in current use: the imperial gallon which is used in the United Kingdom and semi-officially within Canada, the United States liquid gallon and the lesser used United States dry... (gal)	4 qt or
1 peck Peck A peck is an imperial and U.S. customary unit of dry volume, equivalent to 2 gallons or 8 dry quarts or 16 dry pints. Two pecks make a kenning , and four pecks make a bushel.... (pk)	2 gal
1 bushel Bushel A bushel is an imperial and U.S. customary unit of dry volume, equivalent in each of these systems to 4 pecks or 8 gallons. It is used for volumes of dry commodities , most often in agriculture... (bu)	4 pk or 1.244 cu ft
1 (dry) barrel Barrel A barrel or cask is a hollow cylindrical container, traditionally made of vertical wooden staves and bound by wooden or metal hoops. Traditionally, the barrel was a standard size of measure referring to a set capacity or weight of a given commodity. A small barrel is called a keg.For example, a... (bbl)	or 3.281 bu

Small fruits and vegetables are often sold in dry pints and dry quarts. The U.S. dry gallon is less commonly used, and was not included in the handbook that many states recognize as the authority on measurement law. However peck

Peck

A peck is an imperial and U.S. customary unit of dry volume, equivalent to 2 gallons or 8 dry quarts or 16 dry pints. Two pecks make a kenning , and four pecks make a bushel....

s, or bushel

Bushel

A bushel is an imperial and U.S. customary unit of dry volume, equivalent in each of these systems to 4 pecks or 8 gallons. It is used for volumes of dry commodities , most often in agriculture...

s are sometimes used—particularly for grape

Grape

A grape is a non-climacteric fruit, specifically a berry, that grows on the perennial and deciduous woody vines of the genus Vitis. Grapes can be eaten raw or they can be used for making jam, juice, jelly, vinegar, wine, grape seed extracts, raisins, molasses and grape seed oil. Grapes are also...

s, apple

Apple

The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...

s and similar fruit

Fruit

In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...

s in agricultural regions.

Units of mass

Unit	Divisions	SI Equivalent
Most common measures shown in italic font Exact conversions shown in bold font
Avoirdupois
1 grain Grain (measure) A grain is a unit of measurement of mass that is nominally based upon the mass of a single seed of a cereal. From the Bronze Age into the Renaissance the average masses of wheat and barley grains were part of the legal definition of units of mass. However, there is no evidence of any country ever... (gr)	lb
1 dram Dram (unit) The dram was historically both a coin and a weight. Currently it is both a small mass in the Apothecaries' system of weights and a small unit of volume... (dr)	gr
1 ounce Ounce The ounce is a unit of mass with several definitions, the most commonly used of which are equal to approximately 28 grams. The ounce is used in a number of different systems, including various systems of mass that form part of the imperial and United States customary systems... (oz)	16 dr
1 pound Pound (mass) The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement... (lb)	16 oz
1 US hundredweight Hundredweight The hundredweight or centum weight is a unit of mass defined in terms of the pound . The definition used in Britain differs from that used in North America. The two are distinguished by the terms long hundredweight and short hundredweight:* The long hundredweight is defined as 112 lb, which... (cwt)	100 lb
1 long hundredweight	112 lb
1 short ton Short ton The short ton is a unit of mass equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...	20 US cwt or 2000 lb
1 long ton Long ton Long ton is the name for the unit called the "ton" in the avoirdupois or Imperial system of measurements, as used in the United Kingdom and several other Commonwealth countries. It has been mostly replaced by the tonne, and in the United States by the short ton...	20 long cwt or 2240 lb
Troy
1 grain Grain (measure) A grain is a unit of measurement of mass that is nominally based upon the mass of a single seed of a cereal. From the Bronze Age into the Renaissance the average masses of wheat and barley grains were part of the legal definition of units of mass. However, there is no evidence of any country ever... (gr)	lb av or lb t
1 pennyweight Pennyweight A pennyweight is a unit of mass that is equal to 24 grains, 1/20 of a troy ounce, 1/240 of a troy pound, approximately 0.054857 avoirdupois ounce and exactly 1.55517384 grams.... (dwt)	24 gr or 7.776 carats
1 troy ounce Troy ounce The troy ounce is a unit of imperial measure. In the present day it is most commonly used to gauge the weight of precious metals. One troy ounce is nowadays defined as exactly 0.0311034768 kg = 31.1034768 g. There are approximately 32.1507466 troy oz in 1 kg... (oz t)	20 dwt
1 troy pound (lb t)	12 oz t or 13.17 oz av

There have historically been five different English systems of mass: tower, apothecaries'

Apothecaries' system

The apothecaries' system of weights is a historical system of mass units that were used by physicians and apothecaries for medical recipes, and also sometimes by scientists. The English version of the system is closely related with the English troy system of weights, the pound and grain being...

, troy

Troy weight

Troy weight is a system of units of mass customarily used for precious metals, gemstones, and black powder.There are 12 troy ounces per troy pound, rather than the 16 ounces per pound found in the more common avoirdupois system. The troy ounce is 480 grains, compared with the avoirdupois ounce,...

, avoirdupois, and metric

Metric system

. 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 United States. The imperial system, which is still used for some measures in the U.K. and commonwealth 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 by agreement between the U.S., the U.K. 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

Mass

Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

, but the name pound is also applied to measures of force. For instance, in many contexts, the pound

Pound (mass)

The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...

avoirdupois is used as a unit of mass, but in some contexts, the term "pound" is used to refer to "pound-force

Pound-force

The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...

". 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

Dram (unit)

The dram was historically both a coin and a weight. Currently it is both a small mass in the Apothecaries' system of weights and a small unit of volume...

, troy has pennyweight

Pennyweight

A pennyweight is a unit of mass that is equal to 24 grains, 1/20 of a troy ounce, 1/240 of a troy pound, approximately 0.054857 avoirdupois ounce and exactly 1.55517384 grams....

, 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 ounce avoirdupois.

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 United States, 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

Ammunition

Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...

. It was also used to measure medicine and other very small masses.

Grain measures

In agricultural practice, a bushel

Bushel

A bushel is an imperial and U.S. customary unit of dry volume, equivalent in each of these systems to 4 pecks or 8 gallons. It is used for volumes of dry commodities , most often in agriculture...

is a fixed volume of 2150.42 cubic inches. 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

In trade terms a bushel is a term used to refer to these nominal weights.
Although even this varies. With oats, Canada uses 34 lb bushels and the USA uses 32 lb bushels.

Cooking measures

Measure	Australia Australia Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...	Canada Canada Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...	UK	USA	FDA Food and Drug Administration The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
Teaspoon Teaspoon A teaspoon, an item of cutlery, is a small spoon, commonly part of a silverware place setting, suitable for stirring and sipping the contents of a cup of tea or coffee...	5 mL	5 mL	4.74 mL	4.93 mL	5 mL
Dessertspoon			9.47 mL	—	—
Tablespoon Tablespoon A tablespoon is a type of large spoon usually used for serving. A tablespoonful, the capacity of one tablespoon, is commonly used as a measure of volume in cooking...	20 mL	15 mL	14.21 mL	14.79 mL	15 mL
Fluid ounce Fluid ounce A fluid ounce is a unit of volume equal to about 28.4 mL in the imperial system or about 29.6 mL in the US system. The fluid ounce is distinct from the ounce, which measures mass...	—		28.41 mL	29.57 mL	30 mL
Cup	250 mL	250 mL	284.13 mL	236.59 mL	240 mL
Pint Pint The pint is a unit of volume or capacity that was once used across much of Europe with values varying from state to state from less than half a litre to over one litre. Within continental Europe, the pint was replaced with the metric system during the nineteenth century...	—		568.26 mL	473.18 mL	–
Quart Quart The quart is a unit of volume equal to a quarter of a gallon, two pints, or four cups. Since gallons of various sizes have historically been in use, quarts of various sizes have also existed; see gallon for further discussion. Three of these kinds of quarts remain in current use, all approximately...	—		1136.52 mL	946.35 mL	–
Gallon Gallon The gallon is a measure of volume. Historically it has had many different definitions, but there are three definitions in current use: the imperial gallon which is used in the United Kingdom and semi-officially within Canada, the United States liquid gallon and the lesser used United States dry...	—		4546.09 mL	3785.41 mL	–

The most common practical cooking measures for both liquid and dry ingredients in the United States (and many other countries) are the teaspoon, tablespoon and cup, along with halves, thirds, quarters and eighths of these. 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 avdp. of chocolate), stick (e.g., 4 oz avdp. butter) or fruit/vegetable (e.g., a half lemon, two medium onions).

Some common volume measures in English-speaking countries are shown at right. The volumetric measures here are for comparison only.

Units of temperature

Degrees Fahrenheit

Fahrenheit

Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...

are used in the United States to measure temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

s in most non-scientific contexts. The Rankine scale of absolute temperature also saw some use in thermodynamics

Thermodynamics

Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...

. Scientists worldwide use the kelvin

Kelvin

The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

and degree Celsius. Several technical standards are expressed in Fahrenheit temperatures and U.S. medical practitioners often use degrees Fahrenheit for body temperature.

The relationship between the different temperature scales is linear

Linear function

In mathematics, the term linear function can refer to either of two different but related concepts:* a first-degree polynomial function of one variable;* a map between two vector spaces that preserves vector addition and scalar multiplication....

, but the scales have different zero points so that conversion is not simply multiplication by a factor: pure water is defined to freeze at 32 °F = 0 °C and boil at 212 °F = 100 °C at 1 atm

Atmosphere (unit)

The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...

; the conversion formula is easily shown to be:

or inversely as

Other units

1 Board-foot = 2.360 dm³
1 British thermal unit
British thermal unit
The British thermal unit is a traditional unit of energy equal to about 1055 joules. It is approximately the amount of energy needed to heat of water, which is exactly one tenth of a UK gallon or about 0.1198 US gallons, from 39°F to 40°F...

(Btu) ~ 1055 J
1 Calorie
Calorie
The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule...

(cal) = 4.184 J
1 Large calorie (kilocalorie, food calorie) (Cal, kcal) = 4.184 kJ
1 Hand
Hand (unit)
The hand is a non-SI unit of measurement of length, now used only for the measurement of the height of horses in some English-speaking countries, including Australia, Canada, the UK and the USA. With origins in ancient Egypt, it was originally based on the breadth of a human hand...

= 10.16 cm
1 Horsepower
Horsepower
Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...

~ 746 W
1 R-value
R-value (insulation)
The R-value is a measure of thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux through it or R = \Delta T/\dot Q_A.The R-value being discussed is the unit thermal resistance...

(ft²·°F·h/Btu) ~ 0.1761 R_SI (K·m²/W)
1 Slug (mass) = 1 lb_f
Pound-force
The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...

·s²/ft
Various combination units are in common use, including the foot-pound and the psi
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...

; these are straightforwardly defined based on the above basic units.

Other names for U.S. customary units

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

A pejorative name sometimes used by advocates of metrication