Position Size Calculator

Position sizing is the one part of a trading rule that has nothing to do with predicting the market — it is pure arithmetic, and getting it wrong is one of the fastest ways to blow up an otherwise sound strategy. This position size calculator takes the four numbers that actually matter — account size, the percentage of that account you are willing to risk on one trade, your entry price and your stop-loss price — and returns the exact size that keeps the dollar risk on the trade equal to your rule, no more and no less.

The calculation is direct: riskAmount = accountSize × riskPct / 100 is the dollar amount you are willing to lose if the stop is hit. riskPerUnit is simply the absolute distance between entry and stop-loss — a wider stop means a smaller position for the same risk, a tighter stop means a larger one. Dividing riskAmount by riskPerUnit gives positionSize, the number of shares, contracts or units to buy or sell. Because some instruments only trade in whole units and others (forex, crypto, fractional-share brokers) allow decimals, the result shows both: the exact decimal size and the same number floored to a whole unit.

From there, positionValue = positionSize × entryPrice tells you how much capital the trade actually ties up, and dividing that by your account size gives the percentage of your account the position represents. If that percentage passes 100%, the calculator says so plainly — it means the position as sized requires leverage or margin to open, which is worth knowing before you click buy, not after. Add an optional target price and the same risk amount becomes the basis for a reward table: the reward-to-risk ratio (R-multiple) is the distance to target divided by the distance to stop, and the tool lays out what 1R, 2R and 3R look like both as a price level and as a dollar profit — a fast way to see whether a setup's reward justifies its risk before it justifies your attention.

Everything runs locally in your browser with no account data ever leaving your device, and the numbers are unitless so the calculator works the same whether you trade in dollars, euros or any other currency. It answers one question precisely — how big should this position be — and leaves every other trading decision, from whether to take the setup to where exactly to place the stop, to you.