Troy Ounce (oz t)
The troy ounce is a unit of mass used exclusively for precious metals and gemstones, equal to approximately 31.1035 grams. It is heavier than the common avoirdupois ounce (28.35 grams) and is the global standard for trading gold, silver, platinum, and palladium. Every gold price you see quoted - whether on a financial news ticker, a commodities exchange, or a bullion dealer's website - is per troy ounce.
Definition
One troy ounce equals exactly 31.1034768 grams, 480 grains, 20 pennyweights, or 1/12 of a troy pound. It is approximately 9.7% heavier than an avoirdupois ounce (28.3495 grams). The troy ounce is the only troy unit still in common use today. It must not be confused with the avoirdupois ounce used for everyday weighing, as the difference (2.75 grams) has significant financial implications in precious metals trading.
History
The troy ounce takes its name from Troyes, a city in northeastern France that hosted major medieval trade fairs. The troy weight system, used at these fairs for trading precious metals and gems, was adopted by England and eventually standardized across Europe. Unlike the avoirdupois system (16 ounces per pound), the troy system uses 12 ounces per troy pound. England formally adopted troy weights for its coinage in the 15th century. While most troy units have fallen out of use, the troy ounce survives as the universal unit for precious metals trading, codified in commodity exchange rules worldwide.
Common Uses
Gold, silver, platinum, and palladium are priced and traded in troy ounces on every major commodity exchange, including the COMEX, London Bullion Market, and Shanghai Gold Exchange. Central bank gold reserves are reported in troy ounces or metric tons. Bullion coins like the American Gold Eagle, Canadian Maple Leaf, and South African Krugerrand each contain exactly one troy ounce of pure metal. Jewelers and refiners weigh precious metals in troy ounces and pennyweights. Investment portfolios that include physical gold measure holdings in troy ounces.
Did You Know? Facts About Troy Ounce
- A troy ounce of gold is heavier than a regular ounce, but a troy pound (12 troy ounces = 373.24 g) is lighter than an avoirdupois pound (16 ounces = 453.59 g).
- The London gold price fix, established in 1919, has always quoted gold in US dollars per troy ounce.
- Fort Knox reportedly holds about 147.3 million troy ounces of gold, worth hundreds of billions of dollars.
- The word "troy" has nothing to do with ancient Troy - it comes from the French city of Troyes, famous for its medieval trade fairs.
- An American Gold Eagle coin weighs 1.0909 troy ounces total, but contains exactly 1 troy ounce of pure gold - the extra weight is copper and silver alloy.