The volume of a trade measured in lots. 1 standard lot = 100,000 units of base currency. Mini lot = 10,000. Micro lot = 1,000.
In forex, lot sizes determine the dollar value of each pip movement. For EUR/USD: 1 standard lot = $10 per pip, 1 mini lot = $1 per pip, 1 micro lot = $0.10 per pip. Prop firms typically allow fractional lot sizes (e.g., 0.01 lots), giving traders precise control over risk. The correct lot size depends on your account balance, risk percentage, and stop loss distance. Using too large a lot size is the most common way traders breach drawdown limits.