Position size is the single most important number a trader controls. It decides how much money you lose when a trade goes wrong. This page explains what position sizing is, the exact formula, and how to use the calculator above for stocks, forex, crypto and futures.
What is a position size calculator?
A position size calculator turns three inputs — your account balance, the percentage of it you're willing to risk, and the distance from your entry to your stop-loss — into one clear answer: how many shares, lots or contracts to buy or sell. It stops you from risking too much on a single idea, which is the main reason traders blow up accounts.
Why position sizing matters more than your entry
Most beginners obsess over picking the perfect entry. Professionals obsess over position size instead. The reason is simple math: if you risk 50% of your account on one trade and it loses, you need a 100% gain just to get back to even. But if you risk 1–2% per trade, a bad streak of ten losses only costs you a fraction of your capital — you stay in the game long enough for your edge to play out.
The position size formula
For futures, divide by the distance in points multiplied by the contract value:
Worked example
Account: $10,000 · Risk: 2% → money at risk = $200
Entry $100, stop-loss $95 → price distance = $5
Position = $200 ÷ $5 = 40 shares
Account: $5,000 · Risk: 1% → money at risk = $50
Entry 1.1000, stop 1.0950 on EUR/USD → 50 pips × $10 per pip per lot = $500 per lot
Position = $50 ÷ $500 = 0.10 lots (1 mini lot)
What percentage should you risk?
There is no universal answer, but a widely used range is 0.5% to 2% of your account per trade. New traders are usually advised to start at 1% or less until their strategy shows a consistent, positive edge. Risking more than 2% dramatically increases the chance that a normal losing streak empties your account.
Common mistakes to avoid
- Skipping the stop-loss. Position size is meaningless without a defined stop — always set one before you calculate.
- Increasing size after a win. A quick double-up feels great but quietly raises your risk per trade above your rule.
- Ignoring spreads and fees. On tight markets, entry-to-stop distance plus costs is what you actually risk.
- Using leverage without size. Leverage amplifies both profit and loss; position size is what keeps leverage survivable.
Position sizing across markets
Stocks & crypto: results are plain units/shares. Fractional shares matter at low prices — round down to be safe.
Forex: the pip value depends on lot size (1 standard lot = $10 per pip for most pairs), so position size is expressed in lots.
Futures: every contract has a fixed multiplier (contract value per point), so the answer is whole or fractional contracts.