Calculator · free · runs in your browser
Position Size Calculator
Convert a risk percentage into a number of units, given where your stop sits.
When to use itBefore every trade — the one number that decides how much a wrong idea costs.
How to use it
Decide the most you will lose if this trade is wrong, as a share of the account. Many courses use 1% or less while learning.
Put the stop where the idea is proven wrong on the chart — before you size, never after.
Read the units. If the position value is larger than the account, you are borrowing: make sure you meant to.
Result
- Position size (units)
- 20
- Amount at risk
- 100
- Risk per unit
- 5
- Position value (notional)Notional / account size
- 2,000
- Notional / account size
- 0.2×
Formula
amount at risk = account size × risk % ÷ 100risk per unit = |entry − stop|units = amount at risk ÷ risk per unitnotional = units × entry
Assumptions and limits
- The stop is assumed to fill at the price you entered. Gaps and slippage can make the real loss larger.
- Fees, funding and spread are excluded — use the fee calculator for those.
- It says nothing about whether the trade is a good idea, only what size matches the risk you specified.
- Notional above your account size implies leverage, which magnifies both directions.
Understand the number, then use it
The lesson behind it · 9 min
Position Sizing Explained
Position size is derived, not chosen. Once you fix a risk percentage and a stop level, the number of units is arithmetic — and any deviation from it is a decision to take more risk than you said you would.
Read the lesson →
The other calculators
- Risk/Reward Calculator
When deciding whether a setup is worth taking at all, given how often you are right.
- Trading Fee Calculator
When choosing an exchange, and before any strategy that trades small and often.