What Is a Troy Ounce of Gold?
In short
A troy ounce is the unit in which gold and other precious metals are priced internationally; it equals exactly 31.1034768 grams and is heavier than the ordinary avoirdupois ounce.
Precious metals are weighed in troy ounces, a unit of the troy system of weights that has been used for gold and silver for centuries. One troy ounce equals 31.1034768 grams, a value that is exact in the modern metric system, and it is heavier than the avoirdupois ounce used for food and most other goods, which is about 28.35 grams.
The international gold price is quoted in US dollars per fine troy ounce. The word fine means that the price refers to pure gold, whatever the purity of the particular bar; the London Bullion Market Association sets standards for wholesale gold bars, which must have a minimum purity of 995 parts per thousand, and the LBMA Gold Price benchmark is set in dollars per fine troy ounce. In the ISO currency codes gold has the code XAU, which stands for one troy ounce of gold.
To turn an ounce price into a price per gram, divide it by the number of grams in a troy ounce; a price in another currency also needs the exchange rate. A common mistake is to use the 28.35 grams of the ordinary ounce, which understates the grams in a troy ounce and overstates the price per gram by close to 10 percent.
Formula
Price per gram = price per troy ounce / 31.1034768
Troy ounces in a bar = bar weight in grams / 31.1034768The formula is shown as code; N stands for the number of bars or periods.
Figures used in this guide
- 10
- approximate overstatement in percent, derived from the ratio of the two ounce definitions
- 995
- minimum fineness, in parts per thousand, of an LBMA Good Delivery gold bar
- 31.1034768
- grams in one troy ounce, exact by definition
- 28.35
- approximate grams in one avoirdupois ounce
Each number in the text is a definition, a convention or a stated value of the source, not a market observation.
How Lzzo.com shows it
Lzzo.com prices gold per troy ounce in the commodities list and converts the ounce price into grams for gram gold and the coin models with the exact factor above. The ounce price shown is a market reference quote with its source and observation time, and Lzzo.com does not present it as a dealer price. Silver, platinum and palladium are listed per ounce in the same list.
Related guides
Sources
- National Institute of Standards and Technology, NIST Guide to the SI, Appendix B.8: Conversion factors
- National Institute of Standards and Technology, Conversion Factors for Precious Metal Sales
- LBMA, The OTC Guide: The Price
- ISO, ISO 4217 currency codes
Primary and official sources, named as plain text.