Troy weight
Troy weight is a system of
units of
mass customarily used for
precious metals,
black powder, and
gemstones.
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.
Troy ounce
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 percent 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,
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 72~ |
| Ounce (20 pennyweights) | 480 | 31.103 477~ |
| Pennyweight | 24 | 1.555 173 8~ |
| Grain | 1 | 0.064 798 91 |
The Troy pound and ounce were also used in the
Apothecaries' system, but with different further subdivisions.
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.
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Carat (mass)*
Conversion of units*
Mark (weight)
