Troy Ounce
Definition
A troy ounce is the standard unit of weight for precious metals, equal to about 31.1035 grams. It is heavier than the common ounce used for groceries and other goods, which is about 28.35 grams.
When gold and silver are priced “per ounce,” the ounce in question is almost always a troy ounce.
Why it matters
The difference between a troy ounce and a standard ounce is roughly ten percent, which is large enough to matter when you are comparing prices or verifying the weight of a coin or bar. Confusing the two units can lead to miscalculating value.
In practice
Spot prices, coin specifications, and bar weights are all stated in troy ounces. A standard one-ounce gold coin contains one troy ounce of metal, about 31.1 grams. Larger units like the kilogram bar are simply converted from troy ounces at the same per-ounce rate.
Common confusion
The everyday avoirdupois ounce on a kitchen scale is lighter than a troy ounce. If you weigh a coin expecting 28.35 grams, you will get the wrong figure. Always confirm that a scale or listing is using troy weight for precious metals.