A position size calculator turns your account balance, risk percentage, and stop-loss distance into the exact lot size to trade. It exists so your dollar loss stays the same whether your stop is 10 pips or 100 pips wide - the lot shrinks or grows to match the stop, not the other way around.
Pip value per standard lot is $10 for USD-quoted pairs (EUR/USD, GBP/USD, AUD/USD). For other pairs, run the pip value calculator first and paste the result above.
The formula behind it
The calculator runs two short steps. First it finds how many dollars one percent (or whatever you set) of your account is. Then it divides that by the cost of your stop:
Lot size = (balance x risk%) / (stop in pips x pip value per lot)
Because the pip value per standard lot on USD-quoted pairs is $10, a 30-pip stop costs $300 per lot. To risk only $100 you need one-third of a lot. Change nothing but the stop - widen it to 60 pips - and the lot halves automatically so the dollar risk stays at $100.
A worked example
Say you have a $10,000 account and you never risk more than 1% - that is $100 per trade. Your setup needs a 50-pip stop on GBP/USD:
- Risk amount = $10,000 x 1% = $100
- Cost per lot = 50 pips x $10 = $500
- Position size = $100 / $500 = 0.20 lots
Trade 0.20 lots and a full stop-out loses exactly $100. This is the mechanic explained in depth in forex position sizing, and it is exactly what the simulator does for you automatically through auto lot-sizing.
Why fixed dollar risk matters: if you trade the same lot size on every setup, a wide-stop trade quietly risks several times more than a tight-stop one. Sizing from the stop is what makes your 1% risk rule actually mean 1% - every single time.
Prove it on real charts
A calculator gives you the number; a backtest shows you what a hundred of those trades feel like. When you backtest with fixed percentage risk, the simulator sizes every position from your stop for you, so your equity curve reflects disciplined sizing rather than lucky guesses.
Embed this calculator on your site
This calculator is free to embed in any article or tools page. Paste this snippet where you want the widget to appear (the credit line below the frame is the only thing we ask you to keep):
All seven widgets in the free tools collection can be embedded the same way.
Position size calculator FAQ
How do I calculate forex position size?
Take your account balance times your risk percentage to get the dollars you are willing to lose, then divide that by your stop-loss in pips times the pip value per lot ($10 on USD-quoted pairs). The result is your lot size, and it keeps your dollar risk identical no matter how wide the stop is.
What lot size should I use with a $10,000 account?
It depends entirely on your stop, not just the balance. Risking 1% ($100) with a 25-pip stop gives 0.40 lots; the same 1% with a 100-pip stop gives 0.10 lots. Always size from the stop distance, never from the balance alone.
Is the pip value always $10 per lot?
It is $10 per standard lot for pairs quoted in USD such as EUR/USD and GBP/USD. For pairs where USD is the base currency, or for gold and indices, the pip value differs - use the pip value calculator to find the correct figure first.