Position size calculation is the skill that turns a good trade idea into a controlled risk instead of an accident waiting to happen. In this guide you'll learn the position size formula step by step, how to apply it to forex pairs, indices and gold, and which mistakes to avoid when you trade under daily and maximum loss limits.
In short: position size equals the money you're willing to lose divided by your stop loss distance times the value of each pip or point. Decide the risk first, then the stop, and only then the number of lots. Never the other way around.
Why position size matters more than your entry
Plenty of traders spend hours hunting for the perfect entry and a few seconds deciding how many lots to open. That's backwards. Two traders can take the exact same trade, same entry, same stop, and walk away with very different outcomes purely because of size.
Position size is what converts your analysis into money at risk. Too large, and one losing trade eats a big chunk of your loss allowance. Sized consistently, a bad run is just a bad run, something your account can absorb.
On an account with rules, such as an evaluation challenge, this matters even more. It's not only about what you make; it's about never breaching the daily loss or the maximum loss. Position sizing is your main lever to stay inside those limits.
The core position size formula
Every position size calculation starts with three inputs:
- Risk in money: the amount you accept losing if the trade hits your stop. It's your capital multiplied by your risk percentage.
- Stop loss distance: how many pips or points sit between your entry and your stop.
- Pip or point value per lot: how much one full lot gains or loses for each pip or point of movement.
With those three numbers, the formula is:
Lots = Risk in money ÷ (Stop distance × Pip value per lot)
Order matters. You set the risk, then place the stop where your analysis says the idea is wrong, and finally compute the lots. If you pick the lots first and then nudge the stop until the risk "fits," the stop stops meaning anything.
Worked example: forex pairs quoted in USD
On pairs like EUR/USD or GBP/USD, where the dollar is the second currency, one standard lot (100,000 units) is worth roughly $10 per pip. A mini lot (0.10) is $1 per pip and a micro lot (0.01) is $0.10.
Illustrative example:
- $10,000 account.
- 1% risk per trade: $100.
- Stop loss 25 pips from entry.
- Pip value per lot: $10.
Calculation: $100 ÷ (25 × $10) = 0.40 lots.
If price hits the stop, you lose 25 pips × $4 per pip = $100, exactly the 1% you planned.
Now say the technical stop sits further away, at 50 pips: $100 ÷ (50 × $10) = 0.20 lots. The money at risk doesn't change; the size does. That's the whole idea: the market decides the stop, your math decides the size.
When pip value changes: the yen example
When the dollar isn't the quote currency, pip value depends on price. On yen pairs a pip is 0.01, and its value per standard lot is:
Pip value (USD) = 1,000 JPY ÷ pair price
Illustrative example: with USD/JPY at 150.00, one pip is worth 1,000 ÷ 150 ≈ $6.67 per lot.
- $10,000 account, 1% risk = $100.
- 30-pip stop loss.
- Calculation: $100 ÷ (30 × $6.67) ≈ 0.50 lots.
If you used $10 per pip out of habit, you'd open 0.33 lots and risk less than planned. On other crosses the error can run the opposite way, and you'd risk more without noticing. That's why it pays to check each symbol's pip value before you trade.
How to size a gold position
On gold (XAU/USD), the usual contract is 100 ounces per lot. So every $1 move in price equals $100 per lot. Contract size can differ between platforms, so check the symbol information in cTrader before you calculate.
Illustrative example:
- $15,000 account, 1% risk = $150.
- Stop loss $8 away (say, entry at 2,400.00 and stop at 2,392.00).
- Risk per lot: 8 × $100 = $800.
- Calculation: $150 ÷ $800 = 0.1875, rounded down to 0.18 lots.
Gold often moves several dollars in a single session, so technical stops tend to be wide in money per lot. That's why the right size is often small even on a large account.
Position sizing on indices
On indices (such as US30, US100 or GER40) you measure in points rather than pips. The value of one point per lot depends on the contract size each platform uses, and it can differ from one index to another.
Illustrative example (assuming each point is worth $1 per lot; confirm the real value in the symbol information):
- $30,000 account, 1% risk = $300.
- 40-point stop loss.
- Calculation: $300 ÷ (40 × $1) = 7.5 lots.
If your platform valued a point at $10 per lot, the same calculation would give 0.75 lots. The formula stays the same; only the point value changes. This is the classic index mistake: assuming the value from another symbol or another platform.
Quick reference table
| Instrument | Stop unit | Approx. value per lot | Example with $100 risk |
|---|---|---|---|
| EUR/USD, GBP/USD | Pip (0.0001) | $10 per pip | 20 pips → 0.50 lots |
| USD/JPY at 150 | Pip (0.01) | ≈ $6.67 per pip | 20 pips → 0.75 lots |
| XAU/USD | $1 of price | $100 per dollar | $5 → 0.20 lots |
| Index (example) | Point | Depends on contract | Check the symbol |
These values are approximate and meant to show the logic. Before every trade, confirm the exact figure on your platform or use the lot size calculator.
The per-trade risk limit at Funded Profit
At Funded Profit, every trade must stay within a maximum risk of 2.5% of initial capital, both in monetary loss and in lot size. The rules include a formula for maximum lots based on initial capital, leverage (1:100), contract size and price. You'll find it in the risk per trade section.
Two practical points:
- 2.5% is a ceiling, not a target. Most risk plans operate well below it, somewhere between 0.25% and 1%. For more on that, read how much to risk per trade.
- Several trades opened less than 5 minutes apart may be treated as one position. If you split one idea into three quick entries, add up the risk of all of them.
Common lot size mistakes
- Using the wrong balance. Decide whether you size off initial capital or current balance, and stick with it. For account limits, the reference is usually initial capital.
- Forgetting spread and commissions. With a very tight stop, trading costs weigh more. Leave a small buffer or round your size down.
- Rounding up. If the math says 0.47 lots, open 0.47 or 0.46, never 0.50 "to keep it simple."
- Moving the stop after entry. Widening the stop raises your real risk even if size stays the same. Your original calculation no longer holds.
- Using one size for every instrument. 0.50 lots on EUR/USD and 0.50 lots on gold are completely different risks.
- Ignoring correlation. Two positions on closely linked pairs can behave like one bigger position. We cover it in correlation: the hidden risk.
A 5-step routine for every trade
Turn the calculation into a habit with this sequence:
- Set the risk as a percentage according to your plan (for example, 0.5%).
- Convert it to money using your reference capital.
- Place the technical stop loss where your idea is no longer valid.
- Measure the distance in pips or points and confirm the symbol's value per lot.
- Calculate the lots, round down and check you're under the account limit.
Log every calculation in your trading journal. Over time you'll see whether your stops are consistent and whether your actual risk matches the planned one. Pair it with a sound risk/reward ratio and you have the foundation of your risk management.
Trading involves risk, and no formula removes losses. What a well-calculated position size does is make every loss predictable and survivable.
FAQ
What is the formula for position size?
Lots = risk in money ÷ (stop distance × pip or point value per lot). You define the risk and the stop first; the number of lots is the result of the calculation, not the starting point.
How much is one pip worth on a standard lot?
On pairs where the dollar is the quote currency, such as EUR/USD, one standard lot is worth about $10 per pip. On other pairs, like yen crosses, the value moves with price, so check it on your platform.
Should I size off initial capital or current balance?
Both approaches exist, but on accounts whose loss limits are set from initial capital, using that reference keeps the math simpler and consistent with the rules.
What if the calculated size is below the minimum lot?
If the minimum lot already exceeds your planned risk, the stop is too wide for that trade. The prudent choice is to skip it or wait for a setup with a tighter technical stop.