Position size calculator
A position size calculator answers the question most beginners never ask: given where my stop-loss must go, how big can this trade be? Deciding the size from the risk, rather than from the balance or a hunch, keeps any single loss to a planned fraction of the account.
The formula
Position size (lots) = money at risk ÷ (stop distance in pips × pip value per lot)
Worked examples
EUR/USD. Balance $10,000, risk 1%, stop 25 pips away. Money at risk: $100. Pip value on one lot: $10. Size: 100 ÷ (25 × 10) = 0.4 lots, or 40,000 units. If the stop is hit, the loss is 25 × $4 = $100, as planned.
USD/JPY at 150.00. Risk $150 with a 30-pip stop. One pip on one lot is 1,000 ÷ 150, about $6.67. Size: 150 ÷ (30 × 6.667) = 0.75 lots.
Illustrative numbers; use your own balance and current prices.
How to read the result
The answer is the largest position that respects your risk rule, not a target to hit. Round down to the nearest size your provider allows. Notice what happens when the stop gets wider: double the stop distance and the position must halve for the same money at risk. That is why a stop should sit where the trade idea is proved wrong, and the size should adjust to it, never the reverse.
The calculation assumes the stop fills at its level. In fast markets or over a weekend gap it may fill worse, so the real loss can be larger. Check the collateral needed with the margin calculator, and see the pip calculator for how pip values are worked out. Our forex guide puts sizing into the full sequence of a trade.