Lot size and position size calculator
Position size, or lot size, is how many lots you can open to risk only the amount you decided to lose. The maths divides the cash risk by the stop distance multiplied by the value per point. The calculator solves it for forex pairs, gold and indices, in any account currency.
Enter account capital, risk percentage, stop distance in points and point value per lot. The calculator returns the volume to trade and the cash risk, always rounding down.
To go deeper into each part of this calculation: Position size · Risk per trade · How to calculate risk per trade
Why a fixed lot does not work
Always trading the same lot means risking different amounts on every trade, because stop distance changes with volatility and with the instrument. A 15-point stop and a 60-point stop at the same lot are two risks that differ fourfold — and the larger one tends to land on the most nervous day.
Position sizing inverts the order: first you decide how much you accept losing, then the arithmetic says which volume respects that decision. Risk becomes the constant and the lot becomes the consequence.
The formula, step by step
Cash risk = capital × risk percentage. On a 25,000 account at 1%, that is 250.
Volume = cash risk ÷ (stop distance × point value per lot). With a 40-point stop and point value of 10 per standard lot: 250 ÷ (40 × 10) = 0.625 lots.
Round down respecting the instrument step: 0.62 or 0.60 depending on the broker. Never up — rounding 0.625 to 0.63 already breaks the limit you just set.
Add the costs: round-trip commission and swap, if the position crosses the day, come out of the same risk budget. On very short-term trades with tight stops, costs can eat a third of the planned risk.
Point value by asset class
In forex, one pip on a standard lot of a pair quoted in dollars is worth 10 dollars; on cross pairs the value depends on the current quote and on the account currency. On index futures, point value is the contract multiplier. On shares, it is simply the number of shares.
Using one class's value for another is the most frequent spreadsheet error, and it shows up silently: the number looks plausible, it is merely wrong. That is why the calculator asks for point value explicitly instead of guessing from the instrument name.
On a prop firm account
The computed volume still has to pass two filters: the firm's lot cap per trade and the daily loss limit. If three consecutive stops at the computed volume breach the daily limit, the risk percentage is too high for your number of trades per session.
In TCC that check is automatic: the same account shows the firm's limit next to the suggested lot, and history shows how much of the limit each day actually consumed.