Contract size in gold trading

Contract size is the quantity of the underlying asset in one standard lot. For XAUUSD it is most often 100 troy ounces, the same as a COMEX gold futures contract. It is published in the platform’s contract specification alongside the minimum and maximum volume, the volume step, margin requirements, swap rates and trading hours.

How it applies to gold trading

Every money calculation in gold trading starts with contract size. Profit or loss per lot equals the price move multiplied by the contract size. With 100 ounces, a $7 move is $700 per lot. If a platform instead used 10 ounces per lot, the same move would be $70, and a position sizing calculation copied from a 100-ounce platform would be ten times too small.

Contract size also feeds margin and swap. Notional value is price × contract size × lots; margin is notional ÷ leverage; swap is usually quoted per lot per night. Change the contract size and all three change.

Futures traders face the same issue in reverse: the COMEX GC contract is fixed at 100 ounces and the micro MGC at 10 ounces, and the choice between them is a contract-size decision with the same consequences for risk.

A common mistake

Assuming the contract size is 100 ounces without checking, or switching platforms and forgetting that the new one differs. The specification takes a minute to read and removes the biggest source of sizing errors.

See also: Lot, Notional value, Margin, GC futures.

Frequently asked questions