What is troy ounce?

What it means

All gold pricing is per troy ounce, so the XAUUSD quote is the dollar cost of 31.10 grams. The distinction from a normal ounce is not trivia: confusing the two produces a 10% error in any conversion between the quoted price and a physical weight.

Why it matters

The standard contract of 100 troy ounces is what makes gold arithmetic convenient in a trading account. One standard lot is 100 ounces, so a $1.00 move in the quote is $100, and at the 0.01 minimum a $1.00 move is exactly $1.00.

What this changes in practice

That one-to-one correspondence at the minimum lot is genuinely useful when reasoning about risk. It means a stop expressed in dollars of gold price is immediately a stop in dollars of account, per micro lot — no conversion, no pip convention to resolve. See the pip value calculator for the full picture.