Troy ounce

The troy ounce (ozt) is a unit of imperial measure. In the present day it is most commonly used to gauge the weight and therefore the price of precious metals.

The troy ounce is part of the troy weights system derived from the Roman monetary system. The Romans used bronze bars of varying weights as currency. An aes grave weighed equal to 1 pound. One twelfth of an aes grave was called an uncia, or in English an "ounce". Later standardization would change the ounce to 1/16 of a pound (the avoirdupois ounce), but the 1/12 pound troy ounce was retained for the measure of precious metals. At 480 grains, the troy ounce is heavier than the avoirdupois ounce, which weighs 437.5 grains. A grain is 64.7989 milligrams (mg); hence one troy ounce is 31.1035 grams (g), about 10 percent more than the avoirdupois ounce, which is 28.3495 g.

To maintain purity standards and common measures across time, the troy ounce was retained over the avoirdupois ounce in the weighing and pricing of gold, platinum, silver and gunpowder. Likewise, the grain, identical in both the troy and avoirdupois systems, is still used to measure arrow and arrowhead weights in archery along with bullets and powder weights in ballistics. The troy ounce and grain were also common to the apothecaries' system long used in medicine, but have been largely replaced by milligrams.^[1][2]

References

1. ^ "Troy Ounce". WordNet 3.0, Dictionary.com. Princeton University. http://dictionary.reference.com/browse/troy%20ounce. Retrieved 2008-01-10. 
2. ^ "Troy Ounce". Troy Ounce: What is a Troy Ounce?. http://www.troy-ounce.com/. Retrieved 2009-08-31.