how to · beginner
How to Calculate Position Size (The 3-Step Formula Pros Use)
Position sizing is the single most important math in trading — and most beginners skip it entirely. Get this one calculation right and you'll outlast 90% of retail traders before you even pick a strategy.
Position size is how many lots (or units) you trade on a given setup. It's the bridge between your account size, your risk tolerance, and the stop distance the chart is asking for. Done correctly, it makes risk management automatic. Done incorrectly — or skipped entirely — it's the #1 reason retail accounts blow up.
The formula is three numbers. First, your account risk in dollars. This is the maximum you're willing to lose on this single trade. Standard for pros is 1% of account equity. On a $5,000 account, that's $50. On a $25,000 account, that's $250. Second, your stop distance in pips. This comes from the chart — wherever your stop loss is going relative to your entry, measured in pips. Third, the pip value for your instrument. On EUR/USD, one pip on a standard lot = $10. On a mini lot = $1. On a micro lot = $0.10.
The math: lot size = (account risk in dollars) / (stop distance in pips × pip value per pip per lot). Walk through an example. You have a $10,000 account and you want to risk 1% ($100) on a EUR/USD long. Your stop is 25 pips below entry. Pip value on EUR/USD is $10 per pip per standard lot. So lot size = $100 / (25 × $10) = $100 / $250 = 0.4 lots. You'd enter the trade at 0.4 standard lots. If the stop hits, you lose exactly $100. If price runs 50 pips in your favor, you make exactly $200 (a 2:1 R-multiple).
Another example. $500 account, 1% risk ($5), GBP/JPY trade with a 40 pip stop. Pip value on GBP/JPY at current rates is roughly $0.66 per micro lot ($6.60 per mini, $66 per standard). Lot size = $5 / (40 × $0.66) = $5 / $26.40 = 0.19 micro lots. Round down to 0.18 to stay safe. The calculation always rounds DOWN — never UP — to keep you within risk limits.
Do this math on every single trade. Yes, every one. Yes, even when you're confident. Use a calculator (Myfxbook, Babypips, your broker's built-in tool) so it takes 10 seconds. The traders who get destroyed are the ones who eyeball position size or use the same lot size for every trade regardless of stop distance. The traders who survive run the math like a religion. The Candleread desk has never met a long-term profitable trader who doesn't size every trade.
The steps
- 1
1. Decide your account risk percentage
Pros use 1% per trade. 2% is the upper limit. Set this once and apply it to every trade — never vary based on "conviction."
- 2
2. Identify your stop loss from chart structure
Place your stop where the trade is invalidated — behind support, beyond a swing high, etc. Measure the pip distance from entry to stop.
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3. Look up your pip value
On USD-quote pairs (EUR/USD, GBP/USD): $10 per pip per standard lot. Other pairs: use a free calculator from Myfxbook or your broker.
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4. Plug into the formula
Lot size = (account risk in $) / (stop in pips × pip value). Always round DOWN, never up. The result is your exact lot size — no eyeballing.
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5. Verify against margin
Check that the calculated position fits within your account's free margin with comfortable headroom. If margin level would drop below 500%, you're sized too big — reduce stop distance or skip the trade.
Key takeaways
- ✓Position size = (account risk $) / (stop pips × pip value)
- ✓Risk percent stays constant; lot size varies with stop distance
- ✓Always round DOWN, never up
- ✓Use a calculator on every trade — 10 seconds, no exceptions
- ✓Tiny lot sizes are fine; oversizing for psychology is what kills accounts
Frequently asked
Can I just use the same lot size every trade?+
No. Same lot size on different stop distances gives different dollar risks — sometimes 0.5%, sometimes 4%. Your risk should be CONSTANT, which means lot size has to vary with stop distance. That's the whole point of position sizing.
What if the calculated lot size is awkward like 0.07?+
Use it. 0.07, 0.13, 0.43 — whatever the math says. Most brokers accept lot sizes down to 0.01 in 0.01 increments. Don't round up to a "clean" number like 0.1 because that's now risking more than your plan.
What if the math gives me a tiny lot size on a big stop?+
Then your stop is too wide for your account, not too small. Either skip the trade or look for an entry that allows a tighter stop. Forcing oversized trades to "make it worth it" is exactly how accounts blow up.
Should I include the spread in my stop distance?+
Yes. Add the spread to your stop distance when calculating risk. If your stop is 25 pips and the spread is 0.8 pips, treat the effective stop as ~26 pips. It's a small adjustment but it matters on tight stops.