A troy ounce, the only currently used unit of the system, is 480 grains, somewhat heavier than an avoirdupois ounce (437.5 grains). A grain is exactly 64.798 91 mg, hence one troy ounce is exactly 31.103 476 8 g, about 10 per cent more than the avoirdupois ounce, which is exactly 28.349 523 125 g. The troy ounce is the only ounce used in the pricing of precious metals, such as gold and silver, and this is the only remaining use of the troy ounce. In troy weight, there are 12 ounces in a pound, rather than 16 in the more-common avoirdupois system.
A troy pound is 5760 grains (about 373.24 g), rather than 7000 (about 453.59 g).
The use of troy weight for precious metals provides the technical curiosity that an ounce of gold has more mass than an ounce of feathers, but a pound of gold has less mass than a pound of feathers.
The troypound is a unit of mass equalling exactly 0.3732417216 kilogram (or 373.2417216 grams).
Pounds are also used for the force definitions of weight, as well as for other forces, in which the pound force is a unit of force equal to 4.448 newtons.
Over time, the various keepers of the standards redefined pounds in terms of the metric system (which has happened in case of the avoirdupois and troypounds as well as the metric pounds), they were defined in terms of the kilogram, not the dyne or the newton.
In many countries that use the SI or metric system, the pound (or its translation, for example, the German Pfund, the French livre, or the Dutch pond) is used as an informal term for half of a kilogram, therefore for this case the pound is 500 grams.
Pounds are also used for the force definitions of weight, in which the pound force is a unit of force equal to 4.448 newtons.
Although the U.S. National Bureau of Standards[2] has defined the pound as a unit of mass, and the pound-force as a unit of force, this distinction is not widely recognized among working physicists, because the fps system has not been used in physics, even in the U.S., since the early 20th century.
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