Forex Position Size Calculator — Risk-Based Lot Sizing
Never risk more than you intended. Enter your account size, the percentage you're willing to lose, and your stop distance — get the exact lot size to use.
What is position sizing?
Position sizing is the process of deciding how many lots (or units) to trade so that a loss at your stop loss doesn't exceed a pre-set percentage of your account. It's the single biggest lever in trading — most traders who blow up fail at position sizing, not strategy.
How do I calculate position size?
Position size = (account balance × risk %) ÷ (stop loss in pips × pip value per lot). For a $10,000 account risking 1% (= $100) on a 20-pip stop in EURUSD (pip value $10/lot), the lot size is $100 ÷ (20 × $10) = 0.50 lots.
What is the 1% rule?
The 1% rule (sometimes 2%) says never risk more than 1% of your account on a single trade. Over 100 trades with a 50% win rate and 1.5R average winner, a 1% risker survives a 10-trade losing streak with 9.4% drawdown. A 5% risker is down 40%+ in the same streak.
Why does this matter for prop firms?
Prop firms enforce daily drawdown limits (typically 5%) and overall drawdown (8-10%). If you risk 3% per trade and hit 2 stops in one session, you've already breached the daily rule. A position size calculator lets you size trades to fit inside both your risk tolerance and the firm's rules.
Frequently asked questions
What percentage should I risk per trade?
Most professional traders risk 0.25%–1% per trade. Retail traders often risk more, which is why 70-80% of retail accounts lose money. For prop firms with tight drawdown rules, staying below 0.5% per trade is safest.
How does stop loss distance affect lot size?
Inversely. Doubling your stop distance halves your lot size (for the same dollar risk). Wider stops require smaller size; tighter stops allow bigger size. This is why stop placement and position sizing must be decided together.
Does this calculator work for prop firms?
Yes. Size your trades so even two consecutive losers stay well under the daily drawdown cap. If your prop firm has a 5% daily limit, risk no more than 1% per trade.