Pound
This article is about the units of mass; other meanings include:\n*The term
pound used for the unit of
currency in several countries: see
pound (currency). \n*The term
pound, as in
dog pound, as an alternative name for an
animal shelter.\n----\nThe
pound is the name for at least three different
unitss of
mass: \n* the
pound (avoirdupois)\n* the
troy pound\n* the obsolete
imperial pound
There also exists an unofficial
metric pound.
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 gramss). This definition has been in effect since 1959 in the United States. [1] \nIt 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. The 1878 definition in the U.K. defined pound as a mass, but having a very slightly smaller value (equal to approximately 0.453592338 kg) than it does now. 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 (1100-1135). 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 UK. The valuation of precious metals on U.S. exchanges is specified as dollars per troy ounce, although the fact that the troy ounce is implied is usually not stated clearly.
In the context of vegetable etc... sales within Metric countries, a Metric pound (500 g) is 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
\n* History of the pound as a unit of mass: U.S. National Institute of Standards and Technology Official Definition, showing history\n* Official abbreviations and definitions: U.S. National Institute of Standards and Technology Special Publication 811
Category:Units of mass\nCategory:Imperial units\nCategory:US customary units
\n\n\n\n\n\n
