Prop Firm Max Lot Size Calculator
Trade right up to your drawdown limit without going over it. Enter the room you have left and your stop, and get the largest lot size that keeps a single trade inside your remaining cushion.
Cash left before you breach the limit and lose the account.
How much of your room to risk on one trade.
Distance from entry to your stop, measured in pips.
Value of one pip per standard lot ($10 for most USD-quoted pairs).
Risking $2,500.00 on a 20-pip stop, the largest trade that stays inside your room is 12.50 standard lots.
For educational purposes only. Read our risk warning before trading.
How the Max Lot Size Is Calculated
Start from the cash you can afford to lose: your remaining room times the fraction of it you'll risk on this trade. Divide that by the cost of your stop — the stop distance in pips multiplied by the pip value of one standard lot — and you get the largest lot size that keeps the loss inside your room.
Sizing to Your Drawdown
| Concept | What it means |
|---|---|
| Size to drawdown | Risk a fraction of your remaining room, not your full balance — the room is what actually fails the account. |
| Wider stop | A wider stop costs more per lot, so the same room buys you a smaller maximum lot size. |
| Keep a buffer | Never risk 100% of your room on one trade — one stop-out at the limit ends the account with no margin for error. |
Frequently Asked Questions
A prop firm closes your account once your loss crosses the drawdown limit, so the cash left before that point — your room — is the real cap on how much you can lose. This tool sizes your position so that even a full stop-out stays inside that room.
No. Risking 100% of your room on one trade means a single loss ends the account. Most traders risk a small fraction so a losing run still leaves room to recover. Keep the fraction conservative and treat the figure here as the absolute ceiling, not a target.
It is the cash a one-pip move is worth on a single standard lot. For most USD-quoted pairs like EUR/USD that's about $10. JPY and cross pairs differ, so check your broker's contract specs and enter that exact figure for an accurate lot size.
Yes — it works with any firm because you enter your own room. Whether your binding limit is the daily or the overall drawdown, find the smaller cushion first, enter it as your room, and the lot size respects that constraint. Always confirm how your firm measures the limit.
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