Position Size Calculator
Blowing a prop firm evaluation is rarely about picking the wrong direction — it's usually about sizing a position so large that one normal stop-out eats a huge chunk of your daily loss limit. This calculator sizes your position from the risk you actually want to take, not the other way around.
"Units" here means whatever your instrument is quoted in (shares for stocks, contracts for futures, base units for forex/crypto) — this calculator doesn't do lot-size or tick-value conversion for futures/forex, so for those instruments treat "position size" as a raw unit count you still need to convert using your broker's contract specs. This is a starting-point sizing tool, not a substitute for your firm's exact rules on max position size or leverage caps.
Why sizing from risk beats sizing from "how much can I afford"
Most blown accounts aren't the result of a bad trade idea — they're the result of a position sized to what the account could technically afford, not to what the firm's daily loss limit could absorb. Deciding your dollar risk first, then backing into position size from your stop distance, keeps every single trade the same fraction of your drawdown buffer regardless of how volatile the instrument is that day.
Pair this with your firm's actual drawdown rules
This calculator sizes one trade in isolation. To see how much buffer you have left across the whole account before a drawdown breach, use the Drawdown Buffer Calculator alongside it.