What it is
A position size calculator tells you how many lots to trade so that, if your stop loss is hit, you lose only the amount you decided to risk. You enter your account balance, the percentage you are willing to lose, your stop loss distance in pips and the value of one pip. It returns the lot size and the money at risk.
Why it matters
Most traders think about where to enter and where to exit. Far fewer decide how big the trade should be, yet size is what controls how much a losing trade costs you. Two traders can take the same setup with the same stop loss, and one loses 1% while the other loses 10%, only because of the lot size.
Sizing every trade from your stop distance keeps your risk the same on every trade. A wide stop gets a smaller lot, a tight stop gets a larger one, and the money at risk stays the same.
Why traders use it
Traders use it before every entry, right after they have chosen their stop loss. It is also useful for anyone trading a funded or prop account, because those programs usually limit how much you can lose in a day or in total, and the calculator shows whether a planned trade fits inside those limits.
How important is it?
This is one of the few tools we would say you should use on every trade. Risk per trade is the main thing that decides whether a bad run of losses is a small setback or the end of an account. What it does not do is tell you whether a trade is a good one. It controls how much you lose when you are wrong, not how often you are right.
Worked example
With the default numbers, the account is $1,000 and you risk 1%, so the amount at risk is $10. Your stop loss is 20 pips and one pip is worth $10 per standard lot. The lot size is 10 / (20 x 10) = 0.05 lots.
Now say the setup needs a 40 pip stop instead. The same $10 of risk gives 10 / (40 x 10) = 0.025 lots. Most brokers only allow steps of 0.01, so you would round down to 0.02 lots, never up.
Common mistakes
- Using the wrong pip value. It is about $10 per standard lot only on pairs such as EUR/USD. JPY pairs, crosses, gold and indices are different, so check your broker for the real figure.
- Choosing the lot size first and the stop loss second. The stop should come from the chart, and the lot size should then adapt to it.
- Rounding the lot size up. Always round down, so the real risk is never above your limit.
- Forgetting the spread and slippage. In fast markets you can lose a little more than the planned amount.
- Risking too much per trade. There is no perfect number, but many traders keep it to around 1% to 2% or less, so that a string of losses does not do serious damage.
Frequently asked questions
How much should I risk per trade?
There is no single right answer. Many traders risk between 0.5% and 2% of their account on one trade. Beginners and funded prop firm traders are usually better off around 0.25% to 1% so a losing streak stays well inside daily drawdown limits.
Is the pip value always $10?
No. $10 per pip for one standard lot is typical for pairs where USD is the second currency, like EUR/USD. For other pairs the value depends on the exchange rate, and for gold, indices and crypto it depends on the contract. Enter the value from your broker.
How do I calculate lot size for Gold (XAUUSD)?
On most MT4 and MT5 brokers, 1 standard lot of Gold (XAUUSD) is 100 ounces, where a $0.10 move (1 pip) equals $10 per standard lot (or $1 per $0.01 point). Check your broker contract specification and enter that pip value above.
Can I use this for prop firm challenges like FTMO?
Yes. Enter your total prop account size (for example, $10,000 or $100,000) and risk 0.25% to 1% per trade so you can survive multiple consecutive losses without breaching the 5% daily loss limit.
Related trading guides
How to Calculate Position Size, Step by Step
A simple four-step method to work out your lot size from your account balance, risk percentage and stop loss, with worked examples.
What is a Pip and How to Read It?
Learn how to calculate pips, understand pip values, and read forex quotes correctly.
What Is Drawdown and Why Recovery Gets Harder
See how a trading drawdown is measured, why the gain needed to recover grows faster than the loss, and how to limit deep drawdowns.
This page is for education only and is not financial advice. See our disclaimer.