Most new traders spend their energy on entries. Experienced traders spend it on position sizing — because it's the decision that determines how much any single trade can actually cost you. Get this right and a losing streak is survivable; get it wrong and one bad run can end the account.
The short answer
Position sizing is the process of deciding how large a trade to place, based on how much you're willing to lose if it hits your stop. It works backwards from risk: you fix the risk first, then the position size falls out of the math. Your conviction about a trade doesn't change the size — your stop distance and risk percentage do.
The formula
Position size comes from three inputs:
- Account balance and your chosen risk percentage → risk amount in currency
- Stop-loss distance (entry to stop)
- Value per unit of movement for the instrument
Position size = Risk amount ÷ (Stop distance × value per unit)
This is exactly what our Position Size Calculator computes, so you don't have to do it by hand each time.
A worked example
You have a $10,000 account and risk 1% per trade — a risk amount of $100. You're trading EUR/USD with a 20-pip stop loss, where one standard lot is worth about $10 per pip.
- Risk per pip you can afford = $100 ÷ 20 pips = $5 per pip
- Position size = $5 ÷ $10 per pip per lot = 0.5 lots
If your stop were tighter — say 10 pips — the position would double to 1.0 lots for the same $100 risk. The risk stays constant; the size adapts.
Why it matters more than anything else
Consider two traders with the same strategy and a six-trade losing streak:
- Trader A risks 1% per trade → ~6% drawdown, easily recovered.
- Trader B risks 5% per trade → ~26% drawdown, needing a ~35% gain to recover.
Same trades, wildly different outcomes. Sizing — not entries — is what separated them. See What is drawdown? for the recovery math.
Connecting sizing to your stop and risk/reward
Position sizing only works if you have a defined stop loss to size against, and it pairs with risk/reward to shape your expectancy. Together they form the risk-first core covered in the Risk Management Basics guide.
A simple routine
- Fix your risk per trade as a small percentage — and don't change it.
- Place your stop based on the chart.
- Size the position to that stop using the calculator.
- Confirm the risk/reward before entering.
Risk disclaimer: This article is educational content only and is not financial advice. Position sizing manages risk but cannot eliminate it. Trading involves significant risk of loss. Past performance does not guarantee future results. You are responsible for your own decisions.
Frequently asked questions
How do I calculate position size?
Decide your risk amount (a small fixed percentage of your account), then divide it by your stop-loss distance in price terms and the value per unit of movement. Our Position Size Calculator does this for you across forex, gold and indices.
How much should I risk per trade?
Many risk-conscious traders cap risk at roughly 0.5%–1% of the account per trade, so no single trade or short losing streak does serious damage. The exact figure is personal, but small and consistent is the principle.
Why is position sizing more important than the entry?
A good entry with oversized risk can still blow up an account, while a mediocre entry with controlled risk survives. Sizing determines how much a loss actually costs you, which is what keeps you in the game.
Should position size change between trades?
The risk percentage should stay consistent; the position size in lots will vary because it adjusts to each trade's stop distance. Wider stops mean smaller positions, tighter stops mean larger ones — same risk in money terms.