Position Size Calculator
Turn a risk percentage and a stop-loss into an exact position size.
How it works
Position size follows from three numbers you already know: how much you are willing to lose, where you enter, and where you are wrong. The distance to your stop converts a risk in currency into a size in contracts — leverage never enters this part of the calculation.
This is why a wide stop and a tight stop are both fine: the size adjusts so the loss is identical either way. Leverage only determines how much margin you must post to hold that size, not how much you stand to lose.
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How the Position Size Calculator works
A position size calculator converts a risk you are willing to accept into an exact number of contracts. You give it three things — your balance, the percentage you are prepared to lose on this trade, and the distance from entry to stop-loss — and it returns the position size that makes those numbers true.
Why leverage does not belong in this calculation
The most common mistake in leveraged trading is sizing by leverage: 'I'll go 10× on this one.' That decides your margin, not your risk. Two traders both at 10× can have wildly different exposure depending on where their stops sit.
Risk is set by one thing: how much the position loses between entry and stop. Fix the loss first, and the size follows arithmetically. Leverage then only answers a secondary question — how much margin you must post to hold that size. It never changes what the trade costs when you are wrong.
Choosing a risk percentage
One to two percent per trade is the range most professional risk frameworks land on, and the reason is survival rather than growth. At 2% a ten-trade losing streak costs you about 18% of the account — unpleasant but entirely recoverable. At 10% the same streak takes 65%, and recovering that needs a 186% gain.
If you have a measured win rate and payoff ratio, the Kelly criterion gives you a mathematically grounded number instead of a convention. Most traders should then halve it.
Using the result
The calculator returns both a notional size in quote currency and a quantity in the base asset — the quantity is what you type into the order form. It also shows the margin required at your chosen leverage and the minimum leverage that lets your balance carry the position at all.
If required margin exceeds your balance, something has to give: a wider stop with a smaller size, higher leverage, or a smaller trade. The calculator flags this rather than returning a position you cannot actually open.
FAQ
What percentage should I risk per trade?expand_more
One to two percent of the account is the standard professional range. It is low enough that a normal losing streak stays recoverable and high enough that a real edge compounds. Below about 0.5% the edge takes a very long time to show; above 5% ordinary variance starts threatening the account.
Does a wider stop mean more risk?expand_more
No — not if you size correctly. A wider stop produces a smaller position, and the loss at the stop is identical. What a wider stop actually costs you is capital efficiency: the same risk now ties up a different amount of margin.
Does this work for forex and stocks too?expand_more
Yes. The arithmetic is identical for any instrument with a price, a stop and a quantity. For forex you would treat the quantity as units and convert to lots afterwards; the risk logic does not change.
Should I include fees in the risk?expand_more
For most sizing decisions the difference is immaterial, but on high-frequency or high-leverage trading it is not. Check the round-trip cost against your expected profit in the PnL calculator — if fees are a meaningful share of the target, the trade needs rethinking.