Glossary
How to Calculate Position Size From Risk and Stop
How many coins you buy or sell. The formula: risk in money ÷ distance to the stop — then the stop costs exactly 1R.
How it works
The base formula is the same on any market: position size = dollar risk ÷ entry-to-stop distance in price. First, risk per trade is fixed (say, 1% of balance), then the stop is set by the setup's logic, and only after that is position size calculated to produce exactly that dollar loss if that specific stop triggers.
In forex, size is usually converted into lots, which adds pip value into the mix: lots = dollar risk ÷ (stop in pips × pip value per lot). For most XXX/USD pairs, a standard lot (100,000 units of base currency) has a pip value of $10, so mini and micro lots scale that value down proportionally.
Working the calculation backward — picking a lot size first and checking what risk it implies afterward — makes it easy to accidentally risk far more or less than planned. The correct order is always: risk and stop first, position size last.
Example
Account is $5,000, risk per trade is 1% = $50. The EUR/USD stop is 40 pips. Pip value on a standard lot is $10. Size = 50 / (40 × 10) = 0.125 lots. If that stop triggers, the loss comes out to exactly $50.
Common mistake
A common mistake is opening every trade at a fixed size (say, always 0.1 lots) regardless of stop distance. A tight stop then produces a small loss, while a wide stop at the same size produces a risk several times larger than planned.
Read next
Related terms
Frequently asked questions
- Do you need to recalculate position size on every trade?
- Yes, if the stop changes from trade to trade — and it almost always does, moving with volatility and the specific setup's structure.
- What if a broker only allows whole lots or contracts?
- Round the size down so actual risk never exceeds the planned percentage, even if that means trading a slightly smaller size.
Let size and R be calculated for every trade
In the Trading OS journal, risk, position size and the result in R are filled in from entry, stop and exit — with the same formula as here.
No sign-up — the journal runs in your browser; an account is only needed for sync.