Pound (mass)

Pound (mass)

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The pound or pound-mass (abbreviations: lb, lbm, lbm, ) is a unit
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...

 of 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:...

used in the Imperial, United States customary
United States customary units
United States customary units are a system of measurements commonly used in the United States. Many U.S. units are virtually identical to their imperial counterparts, but the U.S. customary system developed from English units used in the British Empire before the system of imperial units was...

 and other systems of measurement
Systems of measurement
A system of measurement is a set of units which can be used to specify anything which can be measured and were historically important, regulated and defined because of trade and internal commerce...

. A number of different definitions have been used, the most common today being the international avoirdupois pound which is legally defined as exactly

The unit is descended from the Roman libra (hence the abbreviation "lb"); the name pound is a Germanic
Germanic languages
The Germanic languages constitute a sub-branch of the Indo-European language family. The common ancestor of all of the languages in this branch is called Proto-Germanic , which was spoken in approximately the mid-1st millennium BC in Iron Age northern Europe...

 adaptation of the Latin phrase libra pondo, 'a pound weight'.

Usage of the unqualified term pound reflects the historical conflation of mass and weight resulting from the near uniformity of gravity on Earth. This accounts for the modern distinguishing terms pound-mass and pound-force.


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 or force.

British pounds

A number of different definitions of the pound have been used in Britain. Amongst these are the avoirdupois pound and the obsolete tower, merchant's and London pounds. The weight of precious metals when given in pounds and/or ounces usually assumes Troy pounds and ounces; these units are not otherwise used today.

Historically the pound sterling
Pound sterling
The pound sterling , commonly called the pound, is the official currency of the United Kingdom, its Crown Dependencies and the British Overseas Territories of South Georgia and the South Sandwich Islands, British Antarctic Territory and Tristan da Cunha. It is subdivided into 100 pence...

 was a tower pound of silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

. In 1528 the standard was changed to the Troy pound.

Avoirdupois pound

The 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...

 pound was invented by London merchants in 1303. Originally it was based on independent standards. During the reign of Henry VIII of England
Henry VIII of England
Henry VIII was King of England from 21 April 1509 until his death. He was Lord, and later King, of Ireland, as well as continuing the nominal claim by the English monarchs to the Kingdom of France...

, the avoirdupois pound was redefined as 7,000 troy grains. Since then, the 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...

 has often been considered as a part of the avoirdupois system. By 1758, two standard weights for the avoirdupois pound existed, and when measured in troy grains they were found to be of 7,002 grains and 6,999 grains.

Imperial Standard Pound

In the United Kingdom, weights and measures have been defined by a long series of Acts of Parliament, the intention of which has been to regulate the sale of commodities. Materials traded in the marketplace must be quantified according to accepted units and standards in order to avoid fraud; the standards themselves must be legally defined so as to facilitate the resolution of disputes brought to the courts; only legally defined measures will be recognised by the courts. Quantifying devices used by traders (weights, weighing machines, containers of volumes, measures of length) are subject to official inspection, and penalties apply if they are fraudulent. The Weights and Measures Act of 1878 marked a major overhaul of the British system, and the definition of the pound given there remained in force until modern times. The pound was defined thus (Paragraph 4) ‘The … platinum weight … deposited in the Standards department of the Board of Trade … shall continue to be the imperial standard of ..weight… and the said platinum weight shall continue to be the Imperial Standard for determining the Imperial Standard Pound for the United Kingdom’. Paragraph 13 states that the weight ‘in vacuo’ of this standard shall be called the Imperial Standard Pound, and that all other weights mentioned in the act and permissible for commerce shall be ascertained from it alone. The First Schedule of the Act gives more details of the standard pound:- It is a platinum cylinder nearly 1.35 inches high, and 1.15 inches diameter, and the edges are carefully rounded off. It has a groove about 0.34 inches from the top, to allow the cylinder to be lifted using an ivory fork. It was constructed following the destruction of the Houses of Parliament by fire in 1834, and is stamped P.S. 1844, 1 lb (P.S. stands for 'Parliamentary Standard'). This definition of the Imperial pound remains unchanged.

Relationship to the kilogram

The 1878 Act says that contracts worded in terms of Metric units will be deemed by the courts to be made according to the Imperial units defined in the Act, and a table of Metric equivalents is supplied whereby, in such cases, the Imperial equivalents may be legally calculated. This effectively defines, for the UK courts and for commerce, the Metric units in terms of Imperial ones. The equivalence for the pound is given as 1 lb = or 0.45359 kg, which would make the kilogram weigh approximately . In 1883, it was determined jointly by the Standards Department of the Board of Trade and the Bureau International that was a better approximation, and this figure, rounded to was given legal status by an Order in Council in May 1898. The Weights and Measures Acts (WMAs) of 1939 and 1958 defined the pound by reference to the WMA of 1878, so as late as 1963 the legal definition of the pound was the same as that given in 1878 (i.e. the platinum standard of 1844).

However, in the WMA of 1963 the pound was redefined for the first time as a mass (not a weight) equal to (to match the definition of the International pound agreed in 1959), and 'For the purposes of any measurement of weight, ... the weight of any thing may be expressed... in the same terms as its mass'. The definition of the pound mass in terms of the Imperial Standard Pound of 1844 was also ratified. This is its present status in the United Kingdom, the same dimension and value having been ratified in the Weights and Measures Act 1985.

United States usage

In the United States, the (avoirdupois) pound as a unit of mass has been officially defined in terms of the kilogram since the Mendenhall Order of 1893. In 1893, the relationship was specified to be per kilogram. In 1894, the relationship was specified to be per kilogram. This change followed a determination of the British pound.

According to a 1959 NIST publication, the international pound differed from the United States 1894 pound by approximately one part in 10 million. The difference is so insignificant that it can be ignored for almost all practical purposes.

International pound

The United States and countries of the Commonwealth of Nations
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...

 agreed upon common definitions for the pound and the 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...

. Since 1 July 1959, the international avoirdupois pound has been defined as exactly .

In the United Kingdom, the use of the international pound was implemented in the Weights and Measures Act 1963.
An avoirdupois pound is equal to 16 avoirdupois 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...

s 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

Troy pound

A troy pound is equal to 12 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...

s and to 5,760 grains, that is grams. Troy weights were used in England by apothecaries and jewellers.

Troy weight
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,...

 probably takes its name from the French market town of Troyes
Troyes is a commune and the capital of the Aube department in north-central France. It is located on the Seine river about southeast of Paris. Many half-timbered houses survive in the old town...

 in France where English merchants traded at least as early as the early 9th century.

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 (WMA 1878). In the United Kingdom, the use of the troy pound was abolished on 6 January 1879 in accordance with the WMA of 1878, though the troy ounce was retained. The troy ounce 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 which uses either avoirdupois pounds or troy ounces, likely never both in the same article, and
  • the mass of Tutankhamun
    Tutankhamun , Egyptian , ; approx. 1341 BC – 1323 BC) was an Egyptian pharaoh of the 18th dynasty , during the period of Egyptian history known as the New Kingdom...

    's sarcophagus
    A sarcophagus is a funeral receptacle for a corpse, most commonly carved or cut from stone. The word "sarcophagus" comes from the Greek σαρξ sarx meaning "flesh", and φαγειν phagein meaning "to eat", hence sarkophagus means "flesh-eating"; from the phrase lithos sarkophagos...

     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.

Tower pound

The system called tower weight was the more general name for King Offa's pound. This dates to 757 AD and was based on the silver penny. This in turn was struck over Arabic dirham
Dirham or dirhem is a unit of currency in several Arab or Berber nations, and formerly the related unit of mass in the Ottoman Empire and Persian states...

s (2d). The pound was based on the weight of 120 Arabic silver dirhams, which have been found in Offa's Dyke
Offa's Dyke
Offa's Dyke is a massive linear earthwork, roughly followed by some of the current border between England and Wales. In places, it is up to wide and high. In the 8th century it formed some kind of delineation between the Anglian kingdom of Mercia and the Welsh kingdom of Powys...

. The same coin weight was used throughout the Hanseatic League
Hanseatic League
The Hanseatic League was an economic alliance of trading cities and their merchant guilds that dominated trade along the coast of Northern Europe...


The mercantile pound (1304) of 6750 troy grains, or 9600 tower grains, derives from this pound, as 25 shilling-weights or 15 tower ounces, for general commercial use. Multiple pounds based on the same ounce were quite common. In much of Europe, the apothecaries' and commercial pounds were different numbers of the same ounce.

The tower system was referenced to a standard prototype found in the Tower of London
Tower of London
Her Majesty's Royal Palace and Fortress, more commonly known as the Tower of London, is a historic castle on the north bank of the River Thames in central London, England. It lies within the London Borough of Tower Hamlets, separated from the eastern edge of the City of London by the open space...

 and ran concurrently with the avoirdupois and troy systems, until it fell out of use and was abolished in 1527.

The tower pound is equivalent to about 350 grams.
1 mercantile pound (15 oz) 9,600 tower grains 6,750 troy grains
1 tower pound (12 oz) 7,680 tower grains 5,400 troy grains
1 tower ounce (20 dwt) = 640 tower grains = 450 troy grains
1 tower pennyweight (dwt)  = 32 tower grains = 22½ troy grains

Merchants' pound

The merchants' pound (mercantile pound, libra mercantoria or commercial pound) was equal to 9,600 wheat grains (15 tower ounces or 6,750 grains). It was used in England until the 14th century for most goods (other than money, spices and electuaries
An electuary is a medicinal paste composed of powders, or other medical ingredients, incorporated with sweeteners to hide the taste, like syrup, honey, jam, etc., for the purposes of oral consumption....


London pound

The London pound is that of the Hansa
Hanseatic League
The Hanseatic League was an economic alliance of trading cities and their merchant guilds that dominated trade along the coast of Northern Europe...

, as used in their various trading places. This is based on 16 of tower ounces, each ounce divided as the tower ounce. It never became a legal standard in England; the use of this pound waxed and waned with the influence of the Hansa itself.

A London pound was equal to 7,200 troy grains (16 tower ounces or, equivalently, 15 troy ounces).
1 London pound 1⅓ tower pounds 7,200 troy grains
1 London ounce = 1 tower ounce = 450 troy grains
1 London pennyweight  = 1 tower pennyweight = 22½ troy grains

Wool pound

The wool pound was equal to 6,992 grains. It was a unit of mass used to measure the weight of wool
Wool is the textile fiber obtained from sheep and certain other animals, including cashmere from goats, mohair from goats, qiviut from muskoxen, vicuña, alpaca, camel from animals in the camel family, and angora from rabbits....


Roman libra

The libra (Latin for "scales / balance") is an ancient Roman unit
Ancient Roman units of measurement
The ancient Roman units of measurement were built on the Hellenic system with Egyptian, Hebrew, and Mesopotamian influences. The Roman units were comparatively consistent and well documented.-Length:Notes...

 of mass that was equivalent to approximately 328.9 grams. It was divided into 12 uncia, or ounces. The libra is the origin of the abbreviation for pound, lb. The commonly used abbreviation lbs to indicate the plural unit of measurement does not reflect Latin usage, in which lb is both the singular and plural abbreviation.

Byzantine litra

The Byzantine litra, more specifically the logarikē or chrysaphikē type used for gold, was equivalent to between 319 and 324 grams.

French livre

Since the Middle Ages, various pounds (livre) have been used in France. Since the 19th century, a livre has referred to the metric pound, 500g.

The livre esterlin was equivalent to about 367.1 gram (3.30393303933039E-05 gr) and was used between the late 9th century and the mid-14th century.

The livre poids de marc or livre de Paris was equivalent to about 489.5 grams (7,555 gr) and was used between the 1350s and the late 18th century. It was introduced by the government of John II
John II of France
John II , called John the Good , was the King of France from 1350 until his death. He was the second sovereign of the House of Valois and is perhaps best remembered as the king who was vanquished at the Battle of Poitiers and taken as a captive to England.The son of Philip VI and Joan the Lame,...


The livre métrique was set equal to the kilogram by the decree of 13 Brumaire an IX between 1800 and 1812. This was a form of official metric pound.

The livre usuelle
Mesures usuelles
Mesures usuelles were a system of measurement introduced by Napoleon I in 1812 to act as compromise between the metric system and traditional measurements...

was defined as 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, but is still used informally.

German and Austrian Pfund

Originally derived from the Roman libra, the definition varied throughout Germany in the Middle Ages and onward. The measures and weights of the Habsburg monarchy
Habsburg Monarchy
The Habsburg Monarchy covered the territories ruled by the junior Austrian branch of the House of Habsburg , and then by the successor House of Habsburg-Lorraine , between 1526 and 1867/1918. The Imperial capital was Vienna, except from 1583 to 1611, when it was moved to Prague...

 were reformed in 1761 by Empress Maria Theresia of Austria. The unusually heavy Habsburg (civil) pound of 16 ounces was later (after the kilogram was defined) found to be 560.012 g. Bavarian
Bavaria, formally the Free State of Bavaria is a state of Germany, located in the southeast of Germany. With an area of , it is the largest state by area, forming almost 20% of the total land area of Germany...

 reforms in 1809 and 1811 adopted essentially the same standard pound. In Prussia
Prussia was a German kingdom and historic state originating out of the Duchy of Prussia and the Margraviate of Brandenburg. For centuries, the House of Hohenzollern ruled Prussia, successfully expanding its size by way of an unusually well-organized and effective army. Prussia shaped the history...

, a reform in 1816 defined a uniform civil pound in terms of the Prussian foot and distilled water, resulting in a Prussian pound of 467.711 g.

Between 1803 and 1815 all German regions west of the River Rhine were French, organised in the départements Roer, Sarre, Rhin-et-Moselle
Rhin-et-Moselle is the name of a département of the First French Empire in present Germany. It is named after the rivers Rhine and Moselle. It was formed in 1798, when the left bank of the Rhine was annexed by France. Until the French occupation, its territory was divided between the Archbishopric...

, and Mont-Tonnerre
Mont-Tonnerre is the name of a département of the First French Empire in present Germany. It is named after the highest point in the Rhenish Palatinate, the Donnersberg. It was the southernmost of four départements formed in 1798, when the west bank of the Rhine was annexed by France...

. As a result of the Congress of Vienna these became part of various German states. However, many of these regions retained the metric system and the French système usuel with the metric pound of precisely 500 g. In 1854 the pound of 500 g also became the official mass standard of the German Customs Union
thumb|upright=1.2|The German Zollverein 1834–1919blue = Prussia in 1834 grey= Included region until 1866yellow= Excluded after 1866red = Borders of the German Union of 1828 pink= Relevant others until 1834...

, but states differed in the way they subdivided it (decimally, in 30 parts or in 32 parts), and local pounds continued to co-exist with the Zollverein pound for some time in some German states. Nowadays, the term Pfund is still in common use and universally refers to a pound of 500 g.

Russian funt

The Russian pound (Фунт, funt) is an obsolete Russian unit of measurement of mass. It is equal to 409.51718 grams.


The Skålpund was a Scandinavian measurement that varied in weight between regions. From the 17th century onward, it was equal to 425.076 grams in Sweden. It was abandoned in 1889 when Sweden switched to the metric system.

In Norway the same name was used for a weight of 498.1 grams, and in Denmark it equalled 471 grams.

In the 19th century Denmark followed Germany's lead and redefined the pound as 500 grams.

20 skålpund = 1 lispund

Jersey pound

A Jersey pound is an obsolete unit of mass used on the island of Jersey
Jersey, officially the Bailiwick of Jersey is a British Crown Dependency off the coast of Normandy, France. As well as the island of Jersey itself, the bailiwick includes two groups of small islands that are no longer permanently inhabited, the Minquiers and Écréhous, and the Pierres de Lecq and...

 from the 14th century to the 19th century. It was equivalent to about 7,561 grains (490 grams). It may have been derived from the French livre poids de marc.

Trone pound

The trone pound is one of a number of obsolete Scottish units of measurement
Obsolete Scottish units of measurement
Scotland had a distinct system of measures and weights until at least the late 18th century, based on the ell as a unit of length, the stone as a unit of mass and the boll and the firlot as units of dry measure...

. It was equivalent to between 21 and 28 avoirdupois ounces (about 600-800 grams).

Metric pounds

In many countries upon the introduction of a 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...

, the pound (or its translation) became an informal term for 500 grams,

The Dutch
Dutch language
Dutch is a West Germanic language and the native language of the majority of the population of the Netherlands, Belgium, and Suriname, the three member states of the Dutch Language Union. Most speakers live in the European Union, where it is a first language for about 23 million and a second...

 pond is an exception. It was officially redefined as 1 kilogram, with an ounce of 100 grams, but people seldom use it this way. In daily life pond is exclusively used for amounts of 500 grams, and to a lesser extent, ons for 100 grams.

In German
German language
German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....

 the term is Pfund, in French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...

Livré-la-Touche is a commune in the Mayenne department in north-western France. Prior to October 6, 2008, it was known as Livré....

, in Dutch pond, in Spanish
Spanish language
Spanish , also known as Castilian , is a Romance language in the Ibero-Romance group that evolved from several languages and dialects in central-northern Iberia around the 9th century and gradually spread with the expansion of the Kingdom of Castile into central and southern Iberia during the...

 and Portuguese
Portuguese language
Portuguese is a Romance language that arose in the medieval Kingdom of Galicia, nowadays Galicia and Northern Portugal. The southern part of the Kingdom of Galicia became independent as the County of Portugal in 1095...

 libra, in Italian
Italian language
Italian is a Romance language spoken mainly in Europe: Italy, Switzerland, San Marino, Vatican City, by minorities in Malta, Monaco, Croatia, Slovenia, France, Libya, Eritrea, and Somalia, and by immigrant communities in the Americas and Australia...

 libbra, and in Danish and Swedish
Swedish language
Swedish is a North Germanic language, spoken by approximately 10 million people, predominantly in Sweden and parts of Finland, especially along its coast and on the Åland islands. It is largely mutually intelligible with Norwegian and Danish...


Though not from the same linguistic origin, the Chinese jin (also known a "catty
The catty , symbol 斤, is a traditional Chinese unit of mass used across East and Southeast Asia, notably for weighing food and other groceries in some wet markets, street markets, and shops. Related units include the picul, equal to 100 catties, and the tael, which is of a catty. A stone is a...

") has a modern definition of exactly 500 grams, divided into ten cun. Traditionally about 605 grams, the jin has been in use for more than two thousand years, serving the same purpose as "pound" for the common-use measure of weight.

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 as the use of the pound is not sanctioned for trade within the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...


Use in weaponry

Smoothbore cannon and carronades are designated by the weight in imperial pounds of round solid iron shot of diameter to fit the barrel. A cannon that fires a six-pound ball, for example, is called a six-pounder. Standard sizes are 6, 12, 18, 24, 32 and 42 pounds; 68-pounders also exist, and other nonstandard weapons use the same scheme. See carronade.

A similar definition, using lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 balls, exists for determining the gauge
Gauge (bore diameter)
The gauge of a firearm is a unit of measurement used to express the diameter of the barrel. Gauge is determined from the weight of a solid sphere of lead that will fit the bore of the firearm, and is expressed as the multiplicative inverse of the sphere's weight as a fraction of a pound . Thus...

 of shotgun
A shotgun is a firearm that is usually designed to be fired from the shoulder, which uses the energy of a fixed shell to fire a number of small spherical pellets called shot, or a solid projectile called a slug...


Conversion between units