Position Size Calculator
Work out how many units to trade so a stop-loss hit costs exactly your intended risk.
Please note: Trading carries substantial risk of loss. These calculators are planning tools, not trading advice, and no position sizing method prevents losses.
What the Position Size Calculator does
Position sizing works backwards from risk. You decide the maximum you are willing to lose, measure the distance from entry to stop-loss, and divide. The result is the only position size where a stopped-out trade costs exactly what you planned.
Formula
Risk amount = Account × Risk % ÷ 100Risk per unit = |Entry − Stop-loss|Position size = Risk amount ÷ Risk per unit
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Account balance | selected currency | Yes | Accepts more than 0. |
| Risk per trade | % | Yes | Percent of the account you accept losing if stopped out. |
| Entry price | selected currency | Yes | Accepts more than 0. |
| Stop-loss price | selected currency | Yes | Accepts more than 0. |
| Currency | one of 10 options | Optional | — |
How to use it
- Choose Currency.
- Enter Account balance, Risk per trade, Entry price and Stop-loss price.
- Select Calculate.
Worked example
A $25,000 account risking 1% per trade, entering at $150 with a stop at $144.
- Account
- 25000
- Risk
- 1
- Entry
- 150
- Stop
- 144
Risk $250 ÷ $6 per unit = 41.67 units, a position worth $6,250.
Frequently asked questions
How much should I risk per trade?
One to two percent is the common professional range. At 2% risk, ten consecutive losses cost about 18% of the account — survivable. At 10% risk, the same streak is close to fatal.
Why not just use a fixed number of shares?
Because a fixed size means your loss varies with every stop distance. Sizing by risk keeps every losing trade the same cost, which is what makes results statistically comparable.
What if the calculated size needs leverage?
Either widen your stop, reduce your risk percentage, or accept that you need margin. Do not simply size up and ignore it.
Method and sources
Method. Position size is the amount of capital at risk divided by the distance from entry to stop. The risk is chosen by the reader as a percentage of account equity; the stop distance comes from the prices entered.
Assumptions
- The stop is executed at the price entered. In practice a gap or a fast market fills worse, so the realised loss can exceed the intended risk.
- The full position is entered at one price rather than scaled in.
Limitations
- Sizing controls the loss on a single trade if the stop holds. It does nothing about correlated positions, overnight gaps, or a sequence of losses.
- No position size makes a trade safe, and none of this is a view on whether the trade is worth taking.