How to Calculate Position Size in Trading
Position sizing is the single most important skill in trading. Learn the exact formula professional traders use to protect their capital and maximize returns.
Skip the math and use our free position size calculator.
Open Position Size CalculatorWhat is Position Sizing?
Position sizing determines how many units of an asset (shares, contracts, lots, or coins) you should buy or sell on any given trade. It's the cornerstone of risk management and the difference between professional traders and gamblers.
Without proper position sizing, even a strategy with a 70% win rate can blow up your account. With proper position sizing, even a strategy with a 40% win rate can be profitable.
The Position Size Formula
The formula for calculating position size is:
Position Size = Risk Amount ÷ Risk Per UnitWhere:
- Risk Amount = The dollar amount you're willing to lose on this trade
- Risk Per Unit = |Entry Price - Stop Loss Price|
Note: Leverage does not affect position size or P&L—it only determines how much margin (collateral) you need.
Step-by-Step Position Size Calculation
Step 1: Determine Your Risk Amount
First, decide how much of your account you're willing to risk on this single trade. The industry standard is 1-2% of your total account.
Example:
Account Size: $10,000
Risk Percentage: 1%
Risk Amount: $100
Step 2: Calculate Risk Per Unit
Find the absolute difference between your entry price and stop loss price.
Example (Long Trade):
Entry Price: $50,000
Stop Loss: $49,000
Risk Per Unit: $1,000
Step 3: Apply the Formula
Risk Amount: $100
Risk Per Unit: $1,000
Position Size = $100 ÷ $1,000
Position Size = 0.1 BTC
Step 4: Verify Your Margin
Make sure you have enough capital to open this position. With 10x leverage, 0.1 BTC at $50,000 (notional value $5,000) requires $500 in margin.
Why the 1% Rule Matters
Risking 10% Per Trade
After 7 consecutive losses, you've lost 52% of your account. You need a 108% return just to break even.
Risking 1% Per Trade
After 7 consecutive losses, you've lost only 6.8%. You need just a 7.3% return to break even.
Common Position Sizing Mistakes
Not using a stop loss
Always define your exit before entering a trade. No stop loss = no way to calculate position size.
Risking too much per trade
Stick to 1-2% maximum. Even with a 60% win rate, you'll face losing streaks.
Confusing leverage with position size
Leverage only affects margin requirements, not your position size or P&L.
Moving stop losses further away
If you move your stop, you must reduce your position size proportionally.
Calculate Your Position Size Now
Ready to apply what you've learned? Use our free position size calculator to instantly calculate the optimal position size for your next trade.