Lot Size for Margin.
Position size has two ceilings — the dollar risk you're willing to lose if the stop hits, and the margin your broker will let you tie up to open the trade. This calculator handles the second. Tell it your equity, leverage, the instrument and the share of equity you're comfortable committing to one position, and it returns the maximum lot size, the margin you'll use, and the free margin left to absorb drawdown. Helpful when you scale up — small accounts blow up because traders forget that margin requirements rise with notional.
Inputs
Account & broker
Conservative: 10-30%. Above 50% leaves little room for drawdown.
Result
Max position
Indicative prices used for margin estimation. Live broker requirements may differ — always confirm in your terminal.
Equity, leverage, lot size
Leverage decides what fraction of notional value the broker requires you to post as margin. 1:100 leverage means 1% of notional. The lot size your account can hold is the lower of what your risk budget allows and what your margin allows.
Formula
MaxLots = (Equity × Utilisation%) ÷ MarginPerLot
MarginPerLot = (ContractSize × Price) ÷ Leverage
- Margin utilisation — keep it under 30%. Higher and a small adverse move gets you stopped out by the margin engine, not your plan.
- Free margin — the cushion you have left. If free margin goes negative the broker liquidates.
- Worked example — $10,000 equity, 1:100 leverage, 30% utilisation, EUR/USD at 1.0850. Margin per lot ≈ $1,085. Max lots = 3,000 / 1,085 ≈ 2.76.
Pair margin sizing with risk sizing.
Use the smaller of the two outputs. Your trade size should respect both constraints.