Position sizing step by step

Position sizing turns your risk rule into an actual trade size. It is simple arithmetic, but small mistakes here can multiply your risk several times over, so it is worth practising until it becomes routine.

The formula

You need four inputs:

• Account balance in your account currency.
• Risk percentage per trade, for example 1%.
• Stop distance in pips: the gap between your entry and your stop-loss.
• Pip value per standard lot in your account currency.

Then:

• Risk amount = account balance × risk %
• Position size in lots = risk amount ÷ (stop distance in pips × pip value per lot)

A quick reminder of the units: a standard lot is 100,000 units of the base currency, a mini lot is 10,000 and a micro lot is 1,000. A pip is 0.0001 for most pairs and 0.01 for pairs quoted in Japanese yen.

Worked example 1: EUR/USD

You have a 10,000 USD account, you risk 1% per trade, and your analysis puts the stop 25 pips from your entry.

Step 1 – risk amount. 10,000 × 1% = 100 USD.

Step 2 – pip value. EUR/USD is quoted in US dollars, so 1 pip on 1 standard lot is 100,000 × 0.0001 = 10 USD.

Step 3 – loss per lot if the stop is hit. 25 pips × 10 USD = 250 USD per standard lot.

Step 4 – position size. 100 ÷ 250 = 0.40 lots, which is 40,000 units of EUR, or 4 mini lots, or 40 micro lots.

Check: 40,000 units × 0.0025 (25 pips) = 100 USD. The loss at the stop matches your 1% risk.

What about margin?

Margin is a separate question from risk. Required margin = position notional ÷ leverage. Using an example price of 1.1000, the notional value is 40,000 × 1.1000 = 44,000 USD. At 30:1 leverage the margin is 44,000 ÷ 30 = about 1,467 USD. That money is set aside as a deposit; it is not the amount you are risking. Your risk is still the 100 USD defined by your stop.

Worked example 2: USD/JPY

Pairs quoted in yen need one extra step, because the pip value is in yen and must be converted to your account currency.

You have the same 10,000 USD account and 1% risk, and this time your stop is 40 pips away. Assume an example USD/JPY price of 150.00.

Step 1 – risk amount. 10,000 × 1% = 100 USD.

Step 2 – pip value in yen. For JPY pairs a pip is 0.01, so 1 pip on 1 standard lot is 100,000 × 0.01 = 1,000 JPY.

Step 3 – convert to USD. 1,000 JPY ÷ 150.00 = about 6.667 USD per pip per standard lot.

Step 4 – loss per lot if the stop is hit. 40 pips × 6.667 USD = about 266.67 USD.

Step 5 – position size. 100 ÷ 266.67 = 0.375 lots. Most platforms allow two decimal places, so you round down to 0.37 lots.

Check: 0.37 × 40 × 6.667 = about 98.67 USD, just under your 100 USD limit.

Notice that the USD value of a yen pip changes as the exchange rate moves. At an example rate of 125.00 it would be 8 USD per lot; at 160.00 it would be 6.25 USD. Always use a current rate when you do this for real.

Common mistakes

Practical habits

• Use a calculator, then check by hand. Many platforms and websites offer position-size calculators. They are useful, but you should be able to sanity-check the answer with the steps above.
• Wider stop, smaller size. If a sound stop is 50 pips rather than 25, your size halves. The money at risk stays the same.
• Allow for costs. Spreads and commission add a little to each loss. Some traders include the spread in their stop distance for this reason.

Remember that a stop-loss is an instruction, not a promise. In fast markets or over weekend gaps, the fill can be worse than your stop price, so actual losses can exceed the planned amount.

Key takeaways

• Position size in lots = risk amount ÷ (stop distance in pips × pip value per lot).
• For USD-quoted pairs, 1 pip on 1 standard lot is 10 USD; for JPY-quoted pairs it is 1,000 JPY, converted at the current rate.
• 10,000 USD at 1% risk with a 25-pip EUR/USD stop gives 0.40 lots.
• Round position sizes down, and always check that the loss at your stop equals your planned risk.
• Margin is the deposit to open a trade; risk is what you lose if the stop is hit.