Pound

For other uses, see Pound (disambiguation).

The pound is the name for at least three different units of mass:

  • the pound (avoirdupois)
  • the troy pound
  • the obsolete imperial pound

There also exists an unofficial metric pound.

Contents

Origins

The Latin word libra describes a Roman unit of weight similar to a pound, and the abbreviation "lb" for the unit of weight and the sign £ (a crossed-out L) for the currency derived from this. The word "pound" itself comes from the Latin pendere, to weigh.

Measurement systems

In the Imperial system (often referred to as the pound-inch system, or the British system in the U.S.) there are two basic pounds defined, and also an obsolete definition of one variant of the pound:

Pound (avoirdupois) or international pound

The pound (avoirdupois) or international pound, abbreviation "lb" or sometimes # in the U.S., is the mass unit defined as exactly 0.45359237 kilograms (or 453.59237 grams). This definition has been in effect since 1959 in the United States. [1] (http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf) It is part of the avoirdupois system of mass units.

In the United States, the pound has been officially defined as a unit of mass and defined in relation to the kilogram since 1893, but its value in relation to the kilogram was altered slightly in 1894, and again to its current value in 1959 (which only differs from the 1894 definition by approximately one part in 10 million).

There are 16 ounces in a pound (avoirdupois). The pound is equal to exactly 7000 grains, where a grain is officially defined as exactly 0.06479891 gram. The legal definition of the pound in the United Kingdom and Canada are the same as in the United States, and were unified to their current value in 1960.

Imperial pound

In the United Kingdom, the pound was similarly 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 old value is sometimes called the imperial pound, and this definition and terminology are obsolete unless referring to the slightly-different 1878 definition.

Troy pound

A pound (troy) is a unit of mass in the U.S., Canada, and UK. The troy pound is a unit of mass equalling exactly 0.3732417216 kilograms. There are 12 troy ounces in a troy pound. A troy pound is equal to exactly 5760 grains, making 1 troy pound equal to exactly 144/175 pounds. It is part of the troy system of mass units.

The troy pound is used for measurements of precious metals such as gold, silver and platinum. Any weight measurements of precious metals always uses troy pounds and ounces, even though you will find that it is not always explicitly stated that this is the case.

One troy pound = 12 troy ounces = 240 pennyweight.

A pennyweight was literally the weight of a penny, as adopted by King Henry II (1154–1189). This was a sterling silver penny weighing 1/240th of a troy pound.

In countries using the metric system

In many countries that use the SI or metric system the pound (or its translation, e.g. the German Pfund, the French livre or Dutch pond) is used as an unofficial term for half of a kilogram, therefore for this case the pound is defined to 500 grams.

Which one is meant?

If neither "avoirdupois" nor "troy" is specified, the international pound (avoirdupois) is meant and is by law the only proper definition in the U.S., U.K., and Canada; the troy pound has been officially abandoned in the U.K. The valuation of precious metals on U.S. exchanges is specified as dollars per troy ounce, although the fact that the troy ounce is used is usually implied. In the context of vegetable etc. sales within Metric countries, a Metric pound (500 g) is usually implied.

Pound-force

The pound, a unit of mass, should not be confused with the pound-force, a unit of force or weight.

External links



da:Pund (masseenhed) de:Pfund es:Libra (unidad de masa) fr:Livre (unité de masse) ja:ポンド (質量) nl:pond pl:Funt

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