Troy ounce

A gold bar weighing one troy ounce

1 troy ounce coin example (1 oz.) (Platinum Eagle)

A Good Delivery silver bar weighing 1000 troy ounces

The troy ounce (ozt) is a unit of imperial measure. In the present day it is most commonly used to gauge the weight of precious metals. One troy ounce is nowadays defined as exactly 0.0311034768 kg = 31.1034768 g. There are approximately 32.1507466 troy oz in 1 kg. One troy ounce is equivalent to approximately 1.09714 avoirdupois ounces.

The troy ounce is part of the troy weights system, many aspects of which were indirectly 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 troy ounce, which is 1/12 of a troy pound (note that a troy pound is lighter than an avoirdupois pound), has been 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 64.79891 milligrams (mg); hence one troy ounce is 31.1034768 grams (g) (exact by definition), about 10 percent more than the avoirdupois ounce, which is 28.349523125 g (exact).^[1][2]

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 projectile (bullet) and propellant (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.^[3]

History

It is a commonly held misconception that the term "troy" ounce originated in the early Middle Ages as a weight unit used at the famous Champagne fairs at Troyes, Champagne. This story originated in England in the 1600s, many centuries after the Champagne fairs had been discontinued. Only slightly less likely is the theory that "troy" is reference of ancient Troy of Anatolia.^[4]

See also

• English unit
• Imperial unit
• Tola (unit)
• United States customary units

References

1. ^ "Troy Ounce". Troy Ounce: What is a Troy Ounce?. http://www.troy-ounce.com/. Retrieved 2009-08-31. 
2. ^ "Statutory Instrument 1994 No. 2867: The Units of Measurement Regulations 1994". http://www.opsi.gov.uk/si/si1994/uksi_19942867_en_1. Retrieved 2010-01-10. 
3. ^ "Troy Ounce". WordNet 3.0, Dictionary.com. Princeton University. http://dictionary.reference.com/browse/troy%20ounce. Retrieved 2008-01-10. 
4. ^ Zupko, Ronald Edward (1977). British Weights and Measures: A History from Antiquity to the Seventeenth Century. University of Wisconsin Press. p. 19. ISBN 978-0299073404.