How to Calculate Position Size in Forex: Complete Guide with Formula
Position sizing is the single most important risk management tool in forex. Trading the wrong lot size can blow your account in a few trades — even with a winning strategy.
The Golden Rule
Never risk more than 1-2% of your account balance on a single trade. This is the professional standard used by almost all consistently profitable traders.
Position Size Formula
Position Size (lots) = (Account Balance × Risk %) ÷ (Stop Loss in Pips × Pip Value per Standard Lot)Step-by-Step Example
Scenario: $5,000 account, risking 1% ($50), 20-pip stop loss on EUR/USD.
- Account: $5,000
- Risk: 1% = $50
- Stop loss: 20 pips
- Pip value for 1 standard lot on EUR/USD: $10
Calculation: $50 ÷ (20 × $10) = $50 ÷ $200 = 0.25 standard lots (2.5 mini lots)
Position Size by Account Size
Here’s how much you can trade with a 20-pip stop and 1% risk:
| Account | Risk (1%) | Pip Value | Position Size |
|---|---|---|---|
| $500 | $5 | $10/standard lot | 0.025 lots (micro) |
| $1,000 | $10 | $10/standard lot | 0.05 lots (mini) |
| $5,000 | $50 | $10/standard lot | 0.25 lots |
| $10,000 | $100 | $10/standard lot | 0.50 lots |
| $50,000 | $500 | $10/standard lot | 2.50 lots |
Adjusting for Different Stop Losses
Wider stops mean smaller position sizes to maintain the same dollar risk:
- 10-pip stop: 0.5 lots (on $5k at 1% risk)
- 20-pip stop: 0.25 lots
- 40-pip stop: 0.125 lots
- 60-pip stop: ~0.08 lots
Common Mistakes
- Trading the same lot size on every trade — A 20-pip stop and a 50-pip stop should have different position sizes
- Ignoring pip value differences — USD/JPY at 152 and EUR/USD have different pip values for the same lot size
- Over-leveraging — Just because your broker allows 0.5 lots on $500 doesn’t mean you should
- Not adjusting for account currency — If your account is in GBP or EUR, pip values need conversion
Prop Firm Position Sizing
Prop firms enforce strict position sizing rules:
- FTMO: Max 0.5% risk per trade during evaluation
- TopStep: Max 1% risk per trade across all accounts
- Apex: Max contract limits based on account size
Always size down during prop firm challenges — the goal is consistency, not home runs. Track your prop firm progress with our prop firm tracker.
Use the position size calculator on our tools page to get your exact lot size in seconds.