Position size calculator Size a trade to a fixed risk, not a hunch
A risk-first way to size a trade works backwards: decide how much you’re willing to lose if the stop hits, and that tells you how big the position can be — not the other way round. Put in four numbers and this tool works out the size in lots and units.
Enter positive numbers in every field.
How to use it
Start with your account balance and the slice of it you’re willing to lose on this one trade — most people who last keep that to 1–2%. Enter the distance to your stop in pips, and the pip value for one standard lot (roughly 10 in your account currency on most pairs). The tool turns your fixed risk into the largest position that respects it: risk the same money on a wide stop and you trade smaller; on a tight stop you can trade bigger.
Risk first, size second
The point of sizing this way is that the loss is decided before the position exists. You pick the money you can afford to be wrong by, and the position bends to fit — instead of picking a size that feels right and discovering the loss afterwards. That single habit is what separates a plan from a hunch.
What the result does and doesn’t mean
This is arithmetic on the four numbers you type, nothing more. It assumes your stop fills exactly where you set it and your pip value is right — it can’t see slippage, weekend gaps, widening spreads or fees, any of which can make the real loss larger than the figure shown. It holds no live prices, and it is not advice to place any trade.
A stop is not a guarantee. In fast or gapping markets your fill can be worse than your stop, so the actual loss can exceed the “amount at risk” here. Size with that in mind, and confirm pip value and fees on your broker’s own page.
The formula, in plain words
The tool works in two steps. First it turns your risk percentage into money: balance multiplied by the risk percent gives the cash you’re prepared to lose if the stop is hit. Then it divides that cash by the loss-per-lot — the stop distance in pips multiplied by the pip value per lot — to get the position size in lots, and multiplies by 100,000 to show it in units. In plain terms: your fixed loss, divided by what one lot would lose over the same stop distance, is how many lots you can hold.
A worked example
Suppose your balance is 5,000, you’ll risk 1% on the trade, your stop is 30 pips away, and the pip value is about 10 per standard lot. One percent of 5,000 is 50 — that’s the money on the line. A single lot losing 30 pips at 10 a pip would lose 300, so 50 ÷ 300 is 0.17 lots, or about 17,000 units. Widen the stop to 60 pips and the loss-per-lot doubles to 600, so the size halves to 0.08 lots — same 50 at risk, smaller position. That trade-off is the whole point: the stop distance, not your confidence, sets the size.
When this number matters — and when it doesn’t
This figure matters because it fixes the loss before the position exists. Decide the money you can be wrong by, and the size bends to fit — the discipline that separates a plan from a hunch. But the number is a ceiling built on clean assumptions, not a promise. It assumes the stop fills exactly where you set it, that your pip value is right, and that nothing else eats the account. It can’t see slippage, weekend gaps, widening spreads or fees, any of which can push the real loss past the “amount at risk” shown. And a comfortable-looking size is not the goal: the goal is a loss you’ve chosen on purpose. Round down rather than up when the maths lands between sizes, and never treat the output as permission to skip the stop.
Common mistakes
- Sizing to a number that feels affordable rather than to a fixed percentage of the balance, so risk creeps up with confidence.
- Entering the pip value for the wrong lot or the wrong account currency, which scales the whole result off.
- Trusting the stop to fill exactly — gaps and fast markets can make the real loss larger than planned.
- Rounding the lot size up to reach a “nicer” number, quietly breaking the risk limit you just set.
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