What is the difference between an American ounce and a troy ounce?

All precious metals are weighed in troy ounces.

The troy ounce is heavier than the typical American ounce.

The troy ounce is about 1.1 American ounces.

A troy ounce equals 31.1 grams.

An American ounce equals 28.35 grams.

A troy pound contains 12 troy ounces.