What is a troy ounce?
The troy ounce is the precious metals market's unit of weight, descended from the medieval trade fair at Troyes, France. It equals 31.1035 grams, versus 28.35 grams for the everyday avoirdupois ounce used for food and postage.
Every number you see in this market, the spot price, a coin's weight, a bar's size, is denominated in troy ounces. When someone says 'gold is at' a figure, they mean per troy ounce.
Why does the distinction matter?
Because mixing the two systems understates weight by nearly 10%. A kitchen scale reading in standard ounces will mislead you; a troy ounce is about 2.75 grams heavier. Reputable dealers state weights explicitly in troy ounces or grams.
It also explains the gram-based products you'll encounter: a 100-gram bar is about 3.215 troy ounces, and a kilo bar is about 32.15 troy ounces.
How does the troy ounce show up in practice?
On every quote and product listing: '1 oz Gold Eagle' means one troy ounce of gold content. If a seller quotes weights in plain ounces or avoids the unit entirely, ask them to state troy weight in writing.