Information about Pound (mass)

"Lbs" redirects here; for the acronym dismbiguation page, see LBS

The pound or pound-mass (abbreviations: lb, ℔, lbm, or sometimes in the United States: #) is a unit of mass (sometimes called 'weight' in everyday parlance) in a number of different systems, including English units, Imperial units, and United States customary units. Its size can vary from system to system. The most commonly used pound today is the international avoirdupois pound.

The distinction between mass and weight (or force) is discussed in the article on weight. In some circumstances, pound is used as the name of a unit of force. That usage is discussed in the article on pound-force, a unit of force equal to the weight of a 1-pound (approximately 0.0311 slug) mass in the standard gravitational field at Earth's surface, g. The actual gravitational field at Earth's surface varies, but the standard gravitational acceleration is usually taken to be 32.174 ft/s².

International pound

Main article: Avoirdupois

The international avoirdupois pound is equal to exactly 453.59237 grams. The definition of the international pound was agreed by the United States and countries of the Commonwealth of Nations in 1958.

In the United Kingdom, the use of the international pound was implemented in the Weights and Measures Act 1963.^[1]

An avoirdupois pound is equal to 16 avoirdupois ounces and to exactly 7,000 grains. The conversion factor between the kilogram and the international pound was therefore chosen to be divisible by 7, and an (international) grain is thus equal to exactly 64.79891 milligrams.

Conversion to other units of mass

The table below sets out the relationships between the avoirdupois pound and:

• the troy pound (see below);
• three other historical pounds (see below): the Tower pound, the merchant pound and the London pound;
• the 500-gram metric pound used in some places for some time during metrication (see below); and
• an International System of Units (SI) unit of mass, the gram.

Each entry is the number of units corresponding to its column required to equal one unit corresponding to its row.

English pounds

	Pounds						Ounces			Grains	Grams
Pound	avdp.	troy	tower	merc.	London	metric	avdp.	troy	tower
Avoirdupois	1	175⁄144	35⁄27	28⁄27	35⁄36	10⁄11	16	14+7⁄12	15+5⁄9	7000	453.59
Troy/ap.	144⁄175	1	16⁄15	64⁄75	4⁄5	3⁄4	13+29⁄175	12	12+4⁄5	5760	373.24
Tower	27⁄35	15⁄16	1	4⁄5	3⁄4	7⁄10	12+12⁄35	11+1⁄4	12	5400	349.91
Merchant	27⁄28	75⁄64	5⁄4	1	15⁄16	7⁄8	15+3⁄7	14+1⁄16	15	6750	437.39
London	36⁄35	5⁄4	4⁄3	16⁄15	1	14⁄15	16+16⁄35	15	16	7200	466.55

Systems of units

When using the pound (mass) as part of the system of units, often called engineering units, that measures time in seconds, distance in feet, and force in pounds-force, a correction factor is required in calculations involving both mass and force due to the fact that 1 pound-force is not the same as 1 lb•ft/sec². See pound-force for more information.

Historical origin

Main article: English unit

The pound as a name for a unit of weight has a long history.

The word “pound” comes from the Latin word pendere, meaning “to weigh”. The Latin word libra means “scales, balances" and it also describes a Roman unit of mass similar to a pound. This is the origin of the abbreviation “lb” or “℔” for the pound.

In the United Kingdom there is a historical link between the pound as a unit of mass and the pound as a unit of currency (the pound sterling), because the unit of currency was defined in the past in terms of a specific quantity of silver.

The avoirdupois pound was invented by London merchants in 1303.

The troy pound takes its name from the French market town of Troyes in France where English merchants traded at least as early as the time of Charlemagne (early ninth century). The system of Troy weights was used in England by apothecaries and jewelers.

Prior to a change during the reign of Henry VIII of England (see below), the avoirdupois pound was based on independent standards which had been measured as about 7,002 troy grains.

During the reign of Henry VIII of England, the avoirdupois pound was redefined as 7,000 troy grains. Since then, the grain has often been considered as a part of the avoirdupois system.

In the United Kingdom, the avoirdupois pound was defined as a unit of mass by the Weights and Measures Act of 1878, but having a very slightly different value (in relation to the kilogram) than it does now, of approximately 0.453592338 kg. (This was a measured quantity, with the independently maintained artifact still serving as the official standard for this pound.) This old value is sometimes called the imperial pound, and this definition and terminology are obsolete unless referring to the slightly-different 1878 definition.

In the United States, the (avoirdupois) pound as a unit of mass has been officially defined in terms of the kilogram since 1893. In 1893, the relationship was specified to be 2.20462 pounds per kilogram. In 1894, the relationship was specified to be 2.20462234 pounds per kilogram. This change followed a determination of the British pound. The current international pound differs from the United States 1894 pound by approximately one part in 10 million.^[2]

Use in commerce

In the United States of America the United States Department of Commerce, the Technology Administration, and the National Institute of Standards and Technology (NIST) have defined the use of mass and weight in the exchange of goods under the Uniform Laws and Regulations in the areas of legal metrology and engine fuel quality in NIST Handbook 130.

NIST Handbook 130 states:

V. "Mass" and "Weight." [NOTE 1, See page 6]

The mass of an object is a measure of the object’s inertial property, or the amount of matter it contains. The weight of an object is a measure of the force exerted on the object by gravity, or the force needed to support it. The pull of gravity on the earth gives an object a downward acceleration of about 9.8 m/s2. In trade and commerce and everyday use, the term "weight" is often used as a synonym for "mass." The "net mass" or "net weight" declared on a label indicates that the package contains a specific amount of commodity exclusive of wrapping materials. The use of the term "mass" is predominant throughout the world, and is becoming increasingly common in the United States. (Added 1993)

W. Use of the Terms "Mass" and "Weight." [NOTE 1, See page 6]

When used in this handbook, the term "weight" means "mass." The term "weight" appears when inch-pound units are cited, or when both inch-pound and SI units are included in a requirement. The terms "mass" or "masses" are used when only SI units are cited in a requirement. The following note appears where the term "weight" is first used in a law or regulation.

NOTE 1: When used in this law (or regulation), the term "weight" means "mass." (See paragraph V. and W. in Section I., Introduction, of NIST Handbook 130 for an explanation of these terms.) (Added 1993) 6"

U.S. federal law, which supersedes this handbook, also defines weight, particularly Net Weight, in terms of the avoirdupois pound or mass pound. From 21CFR101 Part 101.105 - Declaration of net quantity of contents when exempt:

(a) The principal display panel of a food in package form shall bear a declaration of the net quantity of contents. This shall be expressed in the terms of weight, measure, numerical count, or a combination of numerical count and weight or measure. The statement shall be in terms of fluid measure if the food is liquid, or in terms of weight if the food is solid, semisolid, or viscous, or a mixture of solid and liquid; except that such statement may be in terms of dry measure if the food is a fresh fruit, fresh vegetable, or other dry commodity that is customarily sold by dry measure. If there is a firmly established general consumer usage and trade custom of declaring the contents of a liquid by weight, or a solid, semisolid, or viscous product by fluid measure, it may be used. Whenever the Commissioner determines that an existing practice of declaring net quantity of contents by weight, measure, numerical count, or a combination in the case of a specific packaged food does not facilitate value comparisons by consumers and offers opportunity for consumer confusion, he will by regulation designate the appropriate term or terms to be used for such commodity.

(b)(1) Statements of weight shall be in terms of avoirdupois pound and ounce.

See also 21CFR201 Part 201.51 - "Declaration of net quantity of contents" for general labeling and prescription labeling requirements.

From paragraph "a" above, although the avoirdupois pound is a measure of mass, in commerce it is used with the term "Net Weight", because "there is a firmly established general consumer usage and trade custom of declaring the contents of a liquid by weight, or a solid..."

Other pounds

Historically, in different parts of the world, at different points in time, and for different applications, the pound (or its translation) has referred to broadly similar but not identical standards of mass (weight). Some of these other pounds are described below.

Roman libra or pound

Main article: Ancient Roman units of measurement

A Roman libra or pound is an ancient unit of mass that was equivalent to approximately 327 grams. It was divided into 12 uncia, or ounces. The libra is the origin of the abbreviation for pound, lb. The letters lb do not require a period and is used in a singular and plural manner. The abbreviation lbs is not required, but frequently encountered.

Troy pound

Main article: Troy weight

A troy pound is equal to 12 troy ounces and to 5,760 grains. Today, the grain is common to the avoirdupois and troy systems of units of mass, and an international troy pound is equal to 373.241721 grams.

The troy pound is no longer in general use. In Canada, Australia, the United Kingdom, and other places the troy pound is no longer a legal unit for trade. In the United Kingdom, the use of the troy pound was abolished on 6 January 1879. The troy pound is still used for measurements of precious metals such as gold, silver, and platinum, and sometimes gems such as opals.

Most measurements of the mass of precious metals using pounds refer to troy pounds, even though it is not always explicitly stated that this is the case. Some notable exceptions are:

• Encyclopædia Britannica (a U.S. encyclopedia for about a century now) which uses either avoirdupois pounds or troy ounces, likely never both in the same article (which would make an awkward system with 14 7/12 ounces to a pound), and
• the mass of Tutankhamun's sarcophagus lid. This is 110 kilograms. It is often stated to have been 242 or 243 (avoirdupois) pounds but sometimes, much less commonly, it is stated as 296 (troy) pounds.

French livre or pound

Main articles: French units of measurement and Mesures usuelles

The livre (translated as the pound), is a French name for various units of mass since the Middle Ages. The name continues to be used today to refer to a metric pound (see below).

The livre esterlin was equivalent to about 367.1 grams and was used between the late 9th century and the mid-14th century.^[3]

The livre poids de marc or livre de Paris was equivalent to about 7,555 grains or about 489.5 grams and was used between the 1350s and the late 18th century.^[3]. It was introduced by the government of King John II of France.

The livre métrique was set equal to the kilogram or 1,000 grams, by the decree of 13 Brumaire an IX between 1800 and 1812. This was a form of official metric pound (see below).^[3]

The livre usuelle was set equal to 500 grams, by the decree of 28 March 1812. It was abolished as a unit of mass effective 1 January 1840 by a decree of 4 July 1837.^[3]

Russian pound

The Russian pound (Фунт, funt) is an obsolete Russian unit of measurement for weight. It is equal to 409.5124 g.

Jersey pound

A Jersey pound is an obsolete unit of mass used on the island of Jersey from the 14th century to the 19th century. It was equivalent to about 7,561 grains. It may have been derived from the French livre poids de marc (see above).^[4]

Tower pound

Main article: English units

A Tower pound was equal to 5,400 grains. Prior to 1528 the British monetary unit also known as the pound was a Tower pound of silver (worth about $157.50 US* or about £78.75* today). In 1528, the standard was changed to the Troy pound (There are 12 troy oz to the pound, so the same math yields $168 or £84).

• In the above calculations, these numbers were used: Silver is about $14 per troy oz today, and there are 11.25 troy oz in 5,400 grains. There are approximately 2 USD($) to the GBP(£).

This article was also a good description of the tower pound among other old measure systems: [1]

Libra mercatoria or mercantile, merchants' or commercial pound

Main article: English units

A mercantile pound or libra mercantoria, also known as a merchants' pound or commercial pound, is an obsolete unit of mass used in England for most goods (other than money, spices and electuaries) until a point during the 14th century. It was equal to 9,600 wheat grains (equivalent to 6,750 grains). There were 12 tower ounces in a tower pound, and a merchant pound was 15 tower ounces.^[5]

London or mercantile pound

Main article: English units

A London pound was equal to 7,200 grains. A London pound was 16 tower ounces or, equivalently, 15 troy ounces.

Wool pound

Main article: English units

A Wool pound was equal to 6,992 grains. It was a unit of mass used to measure the quantity of wool.^[6]

Scottish or trone pound

Main article: Obsolete Scottish units of measurement

The trone pound is one of a number of obsolete Scottish units of measurement. It was equivalent to between 21 to 28 avoirdupois ounces.

Metric pounds

Main article: kilogram

In many countries upon the introduction of a metric system, the pound (or its translation) became an informal term for half of a kilogram or 500 grams, often following an official redefinition of an existing unit during the 19th century. The Dutch pond is an exception. It was officially redefined as 1 kilogram, with an ounce of 100 grams. If the pound is used in the Netherlands today it is likely to refer to 500 grams; the former definition is no longer used. However, the 100-gram ounce remains in limited use. In daily life pond is exclusively used for amounts of 500-grams, as is ons for 100 grams.

In German the term is Pfund, in French livre, in Dutch pond, in Spanish and Portuguese libra, and in Italian libbra.

Hundreds of older pounds were replaced in this way. Examples of the older pounds are one of around 459 to 460 grams in Spain, Portugal, and Latin America; one of 498.1 grams in Norway; and several different ones in what is now Germany.

Although the use of the pound as an informal term persists in these countries to a varying degree, scales and measuring devices are denominated only in grams and kilograms. A pound of product must be determined by weighing the product in grams. The use of the term pound is usually forbidden for official use in trade.

References

External links

Conversion between units

• Yahoo Conversion Calculator.
• U.S. National Institute of Standards and Technology Special Publication 811
• National Institute of Standards and Technology Handbook 130