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

Contents

Units

Troy ounce

Troy pound

Conversions

Relationship to British coinage

See also

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. The troy grain is used to measure bullet and gunpowder weights in shooting and arrow and arrowhead weights in archery. 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'. In the normal pound that is used now in the United States, there are 14.58 troy ounces.
The above figures apply to England and Wales. In 'Scotland' the Incorporation of Goldsmiths of the City of Edinburgh used a system in multiples of sixteen (''See Assay-Master's Accounts, 1681-1702, on loan from the Incorporation to the National Archives of Scotland''): Thus there were 16 drops to the troy ounce, 16 ounces troy to the troy pound and 16 troy pounds to the troy stone. The Scots had several other ways of measuring precious metals and gems, but this was the common usage for silver and gold.

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 (pound sterling) consisted of 20 shillings, each of which consisted of 12 pennies.
A pound sterling thus weighed 240 pennyweights, or a troy pound of sterling silver.

See also

★ Avoirdupois

★ Carat (mass)

★ Conversion of units

★ Mark (weight)