Troy weight

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Troy weight is a system of units of mass customarily used for precious metals, black powder, and gemstones.

1 History
2 Units
- 2.1 Troy ounce
- 2.2 Troy pound
- 2.3 Conversions
3 Relationship to British coinage
4 See also

History

Troy weight originates from what was called the troy system of mass. Dating back to before the time of William the Conqueror, the name comes from the city of Troyes in France, an important trading city in the Middle Ages.

Units

Troy ounce

A troy ounce 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 31.1034768 g, about 10 percent more than the avoirdupois ounce, which is exactly 28.349523125 g. The troy ounce is the only ounce used in the pricing of precious metals, such as gold, platinum, 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 as in the more common avoirdupois system. The troy ounce may be abbreviated to ozt.

Troy pound

A troy pound is 5760 grains (about 373.24 g, 12 troy ounces), while an avoirdupois pound is 7000 grains (about 453.59 g).

Conversions

Unit	Grains	Grams
Pound (12 ounces)	5760	373.241 721 6
Ounce (20 pennyweights)	480	31.103 476 8
Pennyweight	24	1.555 173 84
Grain	1	0.064 798 91

The Troy pound and ounce were also used in the Apothecaries' system, but with different further subdivisions.

Relationship to British coinage

The troy system was the basis for the pre-decimalisation British system of coinage introduced by King Henry II, in which the penny was literally one pennyweight of silver. A pound sterling thus weighed 240 pennyweights, or a pound of sterling silver. A pound consisted of 20 shillings, each of which consisted of 12 pennies.