Position Size Calculator (forex & futures)

Position sizing answers one question: how many units can I trade so that hitting my stop costs no more than I planned to lose? The formula is: Position size = (Account size × Risk %) ÷ (Stop-loss distance × Value per point/pip).

The logic runs in two steps. First, turn your risk percentage into a dollar amount: account × risk %. Second, work out how much you lose per unit if price travels your full stop distance — that’s stop distance × the value of one point/pip/tick for that instrument. Dividing the first by the second gives the size that makes those two numbers equal. Get either input wrong and the whole calculation is off, so the value-per-move figure matters as much as the percentage.

The risk % input comes from fixed-fractional risk — you risk the same small fraction of your *current* account on every trade, most commonly 1–2%. On a $50,000 account, 1% is $500 and 2% is $1,000. Because the figure is a percentage, your dollar risk shrinks automatically after losses and grows after wins, which is what protects you from a losing streak wiping you out.

The math is unforgiving on this point. Risking 2% per trade, a string of 10 straight losers draws your account down roughly 18%; at 10% per trade, the same streak costs about 65% — and you’d then need a ~185% gain just to get back to even. Smaller fixed risk is the single biggest survival lever a trader controls. Most professionals stay at or below 1%, and prop-firm rules often force you there anyway.

The "value per move" input changes by market, so know which unit you’re in. In forex, price moves in pips; a standard lot (100,000 units) is worth about $10 per pip on most USD-quoted pairs, a mini lot ~$1, a micro lot ~$0.10. In futures, price moves in points made of ticks, and each instrument has a fixed tick value — for example one E-mini S&P 500 (ES) point is $50 (4 ticks of $12.50), and one micro E-mini (MES) point is $5.

So the calculator’s output is denominated in whatever you trade: lots for forex, contracts for futures, shares for stocks. Always confirm the contract specs for your exact instrument and broker — tick values and contract sizes vary, so verify them before sizing a live trade. Rounding also matters: you can only trade whole contracts, so round *down* to stay within your risk.

Say you have a $50,000 account and risk 1% = $500 per trade. You’re trading the E-mini S&P 500 (ES), where one point = $50. Your setup puts a stop 8 points away from entry.

Plug it in: loss per contract at the stop = 8 points × $50 = $400. Position size = $500 ÷ $400 = 1.25 contracts → round down to 1 contract. If you instead traded the micro (MES) at $5/point, one contract loses 8 × $5 = $40 at the stop, so $500 ÷ $40 = 12 contracts — micros let you size precisely on smaller accounts. The same recipe works for forex: replace points with pips and the contract value with your pip value.

Use it before every entry, not after. Set your stop based on the chart — a level the trade is wrong if it breaks — *then* let the calculator tell you the size. Sizing first and forcing a stop to fit is backwards and is how accounts blow up.

Two honest caveats. Slippage and gaps mean your real loss can exceed the planned amount, especially around news or on the open — the calculator assumes you exit exactly at your stop. And it sizes one trade in isolation; if you hold several correlated positions (say long ES and long NQ), your *combined* risk is higher than any single line suggests. This is an educational tool, not financial advice — size conservatively.

Position sizing assumes your fills are clean and your costs are low. On a small stop distance, commissions and spread eat a meaningful share of each trade, and poor fills quietly widen your real risk beyond what you calculated.

NinjaTrader is a popular futures platform for exactly this kind of disciplined sizing: low day-trading margins on micros and E-minis, an ATM (advanced trade management) system that lets you pre-set stop and target brackets, and a free desktop charting tier. If you’re trading futures contracts, executing on a platform built for precise order management makes it far easier to actually trade the size this calculator gives you.