A troy ounce is a measure for gold and other precious metals. It corresponds to 31,1034768 gram. Its abbreviation is “t oz”. Troy ounce only refer to the content of pure gold, excluding other materials. Thus, a 1 ounce gold coin weights slightly more, as physical gold always contains other metals.
The troy ounce has its roots in the historical apothecaries’ system of weights. Therefore it is sometimes, but rarely, also called an apothecary ounce. The term ounce stems from the Italian word for twelfth, “uncia”. Troy received its name from the French city Troyes, an important medieval trade center. The troy ounce is basically the same as the British Imperial troy ounce, adopted as an official weight standard for coinage in 1828. It was in use from 1824 – 1971.
Internationally, the gold price is based on one ounce, with a fineness of .995. Troy ounces are also used to weight platinum, silver and gunpowder.
In the context of precious metals, “troy” is sometimes dropped, so that the weight is just called “ounce” (oz). However, this is not to be confused with the avoirdupois ounce, which has a weight of 28.3495231 grams, 1 troy ounce is equivalent to 1.09714 avoirdupois ounces, or is around 1/10 heavier.
- One troy ounce = 31.1034807 grams
- 32.15 troy ounces = 1 kilogram
- 3.75 troy ounces = 10 tolas (Indian sub-continent)
- 6.02 troy ounces = 5 taels (Hong Kong)
- 1 troy ounce = 480 grains
- 1 troy ounce = 20 pennyweights (North American jewellery trade)
- 1 troy ounce = 155.52 metric carats (precious stones)
The picture shows a 1 ounce US Platinum Eagle bullion coin with a fineness of .9995 and a face value of $100.