What’s the difference between a Troy ounce and a standard ounce?
For historical reasons, precious metals are measured in Troy ounces, a slightly different weight than you would measure an ounce of water in a recipe, for example.
What we think of as “standard” or “regular” ounces–the ones used for produce and cooking in the United States–are known as Avoirdupois (pronounced: a-ver-du-pois) ounces. Troy ounces are reserved for precious metals, gemstones, and gunpowder.
The Troy weight system originated in 15th-century England, and the Avoirdupois system was commonly used in the 13th century and became standardized under later British Imperial and American systems. While some precious metals are denominated using the metric system (g and kg), the Troy system remains very popular to this day.
A Troy ounce is slightly heavier than an Avoirdupois ounce. To summarize:
- 1 Troy oz = 31.103 grams
- 1 Avoirdupois oz = 28.349 grams
Be sure to keep this in mind and do the appropriate conversions if you decide to authenticate your gold and silver using a kitchen scale!
Do 1 oz coins of lower purity (e.g. Krugerrands and Gold American Eagles) still contain an ounce of gold?
Yes – South African Krugerrands, American Eagles, and several other one ounce coins contain 91.67% gold, and are mixed with other metals for strength and durability.
For example, the 1 oz gold Krugerrand is made up of 91.67% gold, and 8.33% copper. The Gold American Eagle is made up of 91.67% gold, 5.33% copper, and 3% silver.
To compensate for the lower percentage of gold, the total weight of these coins is actually slightly greater than 1 Troy ounce (1 1⁄11 Troy ounces in the examples above). This ensures that the actual weight of the gold content is a full Troy ounce.
How Is the Price of Gold and Silver Determined? How Often Do Spot Prices Update?
Gold and silver are traded on various futures markets throughout the world. The major players in the precious metals sector include: the COMEX (Commodity Exchange), Chicago Mercantile Exchange, Hong Kong Mercantile Exchange, the Zurich Gold Market, and the London Bullion Market Association.
When it comes to establishing spot prices for gold, silver and other precious metals, the COMEX is the largest and most commonly referenced of the above futures exchanges.
In the 1990s, the New York Mercantile Exchange (NYMEX) merged with the COMEX. In addition to the regular COMEX trading hours, gold and silver futures continue to trade on exchanges in different time zones around the world. Except for weekends, the spot price of gold and silver will continue to update nearly 24 hours per day.
COMEX trading hours are Sunday – Friday 5:00 p.m. – 4:00 p.m. CST, with a 60-minute break each day at 4:00 p.m. CST.