Position Size Calculator
Let the math pick your lot size, not your gut.
The single most important calculator in retail trading. Input your account balance, the percentage you're willing to risk, and where your stop loss sits. This tool returns the exact lot size that matches your risk tolerance — every time.
On your broker, enter the mini lots figure in the "volume" or "size" field.
What it is
A position size calculator takes three numbers (account balance, risk percent, stop distance in pips) and tells you the correct lot size so that if your stop is hit, you lose exactly the amount you planned to risk — not more. It's the math that separates discretionary gamblers from rule-following traders. Pros run this calculation on every single trade, no exceptions.
When to use it
Every time you open a trade. Before you click buy, you should know three things: how much you're willing to lose, where your stop is, and the exact lot size that matches both. Skipping this step is how accounts blow up — traders pick lot sizes based on vibes, then find out their 'small risk' was actually 8% of the account.
The formula
Risk in dollars = Account balance × (Risk % ÷ 100) Lot size = Risk in dollars ÷ (Stop distance in pips × Pip value per lot) Example: Account: $5,000 Risk: 1% = $50 Stop: 30 pips EUR/USD pip value: $10 per standard lot Lot size = $50 ÷ (30 × $10) = 0.167 standard lots (≈ 1.67 mini lots)
How to use it
- 1. Decide your risk percentage before you look at the chart
The professional standard is 1% per trade. Never higher than 2%. If you risk 1% per trade you would need to lose 50 trades in a row to blow up — which is a strategy problem, not a sizing problem.
- 2. Place your stop loss based on market structure
Your stop goes where the trade idea is invalidated — below a swing low for a long, above a swing high for a short. Never use a random dollar amount for stop placement. The market does not care what you're willing to lose.
- 3. Count the pips from your entry to your stop
This is the 'stop distance' input. A stop 30 pips below your entry is a 30-pip stop. On a USD/JPY trade with a 45-pip stop, enter 45 here.
- 4. Match your pair's pip value
USD-quote pairs (EUR/USD, GBP/USD) are $10 per pip per standard lot. JPY-quote pairs are ~$6-9 depending on the current JPY rate. The calculator handles this — just pick the right pair preset.
- 5. Enter the returned lot size on your broker platform
The 'standard lots' number goes in the volume/size box on your broker. If your platform uses mini lots (0.1) or micro lots (0.01) by default, use that column instead.
Common mistakes
- ✗Picking lot size based on emotion — 'this setup looks great, let me size up.' The math does not care how confident you feel.
- ✗Using a tight stop to justify an oversized position. A 5-pip stop on a setup that needs 30 pips to breathe will get hunted. Your stop goes where the idea invalidates, not where your math wants it.
- ✗Risking more than 2% per trade. A string of five 2% losses draws the account down 10%. Five 5% losses draws it down 23%. The math is brutal.
- ✗Ignoring correlation. If you're long EUR/USD and GBP/USD at 1% each, your real correlated risk is closer to 1.7% because both pairs move on dollar strength.
- ✗Forgetting to account for spread. A 10-pip spread on a 30-pip target means you need a 40-pip move to hit target, not 30. Size for the real stop distance including spread.