How to calculate lot size in forex
Your lot size should come from your risk, not the other way round. Decide how much of the account you are willing to lose if the stop is hit, measure the stop in pips, then work out how many lots make those two numbers match.
The calculator does this for you and converts the pip value into your account currency, so a GBP account trading USD/JPY gets the right answer without any manual conversion. It always rounds down to the nearest 0.01 lots, so you never risk more than you set.
Worked example
You have a £10,000 account and risk 1% per trade, which is £100. You want to buy EUR/USD with a 15 pip stop.
- One standard lot of EUR/USD is worth $10 per pip.
- At a GBP/USD rate of about 1.33, that is roughly £7.50 per pip.
- £100 ÷ (15 pips × £7.50) = 0.89 lots, which rounds down to 0.88 lots.
If the stop is hit, you lose about £99. If you widened the stop to 30 pips, the same £100 risk would mean halving the position to 0.44 lots.
Standard, mini and micro lots
| Lot | Size | Units | Pip value on EUR/USD |
|---|---|---|---|
| Standard | 1.00 | 100,000 | $10.00 |
| Mini | 0.10 | 10,000 | $1.00 |
| Micro | 0.01 | 1,000 | $0.10 |
Why traders get position sizing wrong
The most common mistake is keeping the same lot size on every trade. A 10 pip stop and a 40 pip stop at the same size are completely different risks: the second trade loses four times as much. Sizing from the stop keeps every loss the same size, which is what makes your results comparable and your drawdowns predictable.
The other mistake is sizing by feel after a few losses. Revenge trades are almost always oversized. Running the numbers before every trade takes the emotion out of the decision.