Calculator
Lot Size Calculator
Estimate position size from balance, risk, stop loss, and instrument.
Contract value: $100 per 1.0 price move · 100 oz per 1.00 lot
Forex, metals and crypto lot sizes are standardized across the listed brokers and prop firms.
Estimate
- Lot size estimate
- 0.10
- Risk amount
- $100
- Stop distance
- 10 (0.25%)
- Mini lots
- 1.0
- Micro lots
- 10
- Position size · risk per 1.00 lot
- 10 oz · $1,000 at stop
Formula: (balance × risk %) ÷ (stop distance × contract value per 1.00 lot). This does not include commission, spread, slippage, or unusual broker contract sizes — always confirm contract specs with your broker.
How the lot size calculator works
A lot size calculator turns your risk tolerance into an exact position size. Instead of guessing how many lots to trade, you enter your account balance, the percentage of the account you are willing to risk, your stop-loss distance and the instrument — and it returns the position size that keeps your loss within that limit if the stop is hit.
For prop firm traders this matters even more than for retail traders. Most evaluations cap your daily and total drawdown, so a single oversized trade can breach the account and end the challenge. Sizing every position from a fixed risk percentage is the simplest way to stay inside those limits while still letting your winners run.
To use it, enter your current balance, choose a risk percentage (many funded traders use 0.5% to 1%), type the stop-loss distance in pips and pick the instrument. The result is the lot size to place so that hitting your stop costs you exactly the risk amount you chose — no more.
Frequently asked questions
How is lot size calculated?
Lot size = (account balance × risk %) ÷ (stop-loss in pips × pip value). The pip value depends on the instrument and your account currency, which the calculator converts for the major forex pairs, indices and metals.
What risk percentage should I use on a prop firm challenge?
Many funded traders risk 0.5%–1% per trade. A lower risk per trade means more losing trades before you approach the daily or maximum drawdown limit, which is usually the safer way to pass an evaluation.
Does lot size change with account size?
Yes. Because risk is a percentage of the balance, the same setup uses a larger position on a $100K account than on a $25K account. Re-check your lot size whenever your balance changes.
Important