The position size formula
Every position sizing decision comes down to three inputs: how much you're willing to lose in dollars, how far away your stop sits, and what each pip is worth. The formula that ties them together is the same one used across the industry:
Worked example: a $10,000 account risking 1% is putting $100 on the line. With a 50-pip stop on EUR/USD, where one pip is $10per standard lot, that's $100 ÷ (50 × $10) = 0.20 lots. Widen the stop to 100 pips and the correct size halves to 0.10 lots — the dollar risk stays at $100 either way.
That last sentence is the part most traders skip. Position size and stop distance move in opposite directions. Keeping lot size fixed while moving your stop means your real risk changes on every trade, which is one of the most common reasons results look random even when the strategy is sound.
Lot sizes explained
| Lot type | Units | Approx. pip value (USD pairs) |
|---|---|---|
| Standard | 100,000 | $10.00 |
| Mini | 10,000 | $1.00 |
| Micro | 1,000 | $0.10 |
| Nano | 100 | $0.01 |
A pip is the smallest standard price increment: 0.0001 on most pairs, 0.01 on JPY pairs, and for gold most brokers quote in $0.10moves. Pip value also depends on your account currency and the pair's quote currency, which is why the JPY and metals presets above are approximations — check your broker's contract specs for exact figures.
How much should you actually risk?
- 0.5–1% — where most risk management guidance puts newer traders. Survives long losing streaks.
- 2% — commonly cited as the ceiling, and only with a proven track record.
- Above 3% — mathematically fragile. A run of six losses takes roughly a fifth of the account.
On a prop firm challenge, go lower.A 5% daily loss limit means three 1.5% losses in one session already puts you close to a breach — and the breach ends the account regardless of how good the rest of the month looked. If you're running an evaluation, check your remaining buffer with the prop firm challenge calculator before sizing up.