An in-depth guide
Forex position size and margin: two separate calculations
Calculate lots from a risk budget and stop distance, allow for commission and slippage, then check margin. Worked EUR/USD and yen-pair examples keep the units explicit.
Trade size and margin answer different questions
Risk-based position size comes from the planned loss to the stop. Required margin comes from exposure and account terms. A trade can pass one calculation and fail the other: a position within the risk budget may need more available margin, while high leverage can permit a position whose loss is too large.
We will use a hypothetical USD 5,000 account and a 1% risk budget, or USD 50. That percentage is an arithmetic assumption, not a recommendation. First calculate size from estimated entry and exit prices, then add costs, and finally check margin. An ordinary stop does not guarantee that the actual loss will end at exactly the calculated amount.
Convert pips and lots into money
Under the convention that one EUR/USD lot is 100,000 euros, a pip of USD 0.0001 per euro is worth USD 10 per lot. At a tenth of a lot, it is worth one dollar. Units matter: a quantity of euros multiplied by a price change quoted in dollars per euro produces a dollar profit or loss.
Check the symbol specification for contract size, volume step and price increment. A pip is not always the last displayed digit; a more precise quote can include a fractional pip. For metals, indices or accounts displaying other units, do not automatically copy the 100,000 multiplier. Similar product names do not guarantee identical specifications at two brokers.
EUR/USD example: size the position to the stop
Assume a buy filled at 1.1000 and an estimated stop exit at 1.0980. The distance is USD 0.0020 per euro, or 20 pips. For this exercise, these are execution prices on the two sides of the trade, not two mid-prices. Do not add another spread to that distance.
The price loss per lot is 20 × 10 = USD 200. A USD 50 budget divided by USD 200 gives 0.25 lots, representing 25,000 euros. This is before commission, financing and slippage. Doubling the stop distance to 40 pips gives 0.125 lots. With a 0.01-lot trading step, round down to 0.12 lots to stay within the price-loss budget.
Allow for commission and slippage without promising a loss cap
Add a hypothetical USD 7 per-lot round-trip commission and a hypothetical 2-pip slippage allowance. At 0.25 lots, the USD 50 price loss plus USD 1.75 commission already exceeds the budget before the allowance. The arithmetic response is to recalculate volume.
Per lot, the calculation becomes USD 200 to the stop + USD 7 commission + USD 20 allowance = USD 227. Dividing 50 by 227 gives about 0.2203 lots. Rounding down to a 0.01-lot step gives 0.22 lots: USD 44 of price loss, USD 1.54 commission and USD 4.40 allowance, totalling USD 49.94. Actual slippage can exceed the allowance; this is a planning estimate, not a maximum-loss guarantee.
Now calculate margin for the same exposure
Return to the original 0.25-lot size to isolate the effect of leverage. At the hypothetical rate of 1.1000, 25,000 euros represent USD 27,500 of exposure. In a simple margin model, divide exposure by the permitted leverage ratio for that symbol after aligning currencies.
Scroll the table horizontally to read every column.
| Hypothetical leverage | Required margin | Price loss over 20 pips |
|---|---|---|
| 1:30 | About USD 916.67 | USD 50 |
| 1:100 | USD 275 | USD 50 |
Leverage changes margin, but not the pip value of the same position. These ratios are not promises of availability from any provider. Exposure tiers, other positions and product terms may alter actual margin requirements.
When quote currency differs from account currency
For a yen-quoted pair, the usual pip size is JPY 0.01. At 100,000 units of base currency, that is JPY 1,000. In a USD account, assuming a hypothetical USD/JPY conversion rate of 150, divide 1,000 by 150 to obtain about USD 6.67 per pip. Automatically using USD 10 would distort the sizing calculation.
The conversion rate can move before closing, so pip value in the account currency is not always constant. Also check whether the platform already displays it in account currency. Converting it twice introduces another error. In a general calculator, make sure price distance, multiplier and risk budget produce the same money unit before relying on the displayed size.
Free margin is not a loss budget
Balance records amounts booked to the account; equity also reflects open positions. Free margin depends on equity and margin already committed. Losses elsewhere in the account can reduce that headroom without any change to the new trade.
Check the whole account, not just the next order ticket. Depending on account terms, a margin closeout can occur before the planned stop. Several trades sharing the same risk driver are not necessarily diversification: positions across pairs that all depend on the same dollar direction can lose together. Sizing one trade is only part of budgeting risk across the account.
Use the calculator without mixing units
In the position-size calculator, first select USD as the currency label. You can illustrate the basic example with capital of 5,000, risk of 1%, entry at 1.1000, stop at 1.0980, a 100,000 multiplier and a 0.01 quantity step. With prices in dollars per euro and quantity in lots, the basic result is 0.25 lots. The calculator does not automatically add a slippage allowance or calculate your broker's margin terms.
Before acting, match the specification and check the account's margin and cost display. The Raw versus Standard guide develops the commission calculation. For futures, use the ticks and margin guide, where contract units differ. Changing interface language does not change account terms or establish eligibility.
