Forex Position Size Calculator

A position size calculator reverses the usual question. Instead of choosing a lot size and hoping the loss is bearable, you choose the loss first and let the arithmetic set the size. It is the single habit most closely linked to staying in the market long enough to learn.

The formula

The pip value per lot is $10 for pairs quoted in US dollars. For other pairs the calculator converts it using the price you enter, as the pip calculator does.

A worked example

Illustrative figures: an $8,000 account, 1.5% risk per trade and a 40-pip stop on EUR/USD.

1. Risk amount: $8,000 × 1.5% = $120.
2. Loss per standard lot at the stop: 40 pips × $10 = $400.
3. Position size: $120 ÷ $400 = 0.30 lots.

If the stop is hit, the loss is about $120 before costs. Widen the stop to 60 pips and the size falls to 0.20 lots; the money at risk stays the same.

Reading the result

Round the answer down to the nearest size your provider allows, never up. The calculation assumes the stop fills at its exact level; in fast markets or over a weekend gap, the fill can be worse, so the real loss can exceed the plan. Spreads and commissions also add to it.

Check the margin the position needs with the margin calculator. A correctly sized position can still be refused, or closed early, if the account lacks the margin to support it.