How to Calculate Lot Size in MT5

Start with cash risk

Percentage risk is only useful after it is converted into the account currency. For a $1,000 balance and 1% risk, the cash-risk target is $10. For a $2,500 balance and 10% risk, it is $250.

cash risk = account balance × (risk percentage ÷ 100)

This is the target loss at the planned stop, before spread, commission, slippage or a price gap. Those costs can make the actual result different.

Divide by the cost of the stop

Next, calculate how much one lot would lose across the chosen stop distance. Multiply the stop in pips by the value of one pip at 1.00 lot, then divide the cash risk by that amount.

lot size = cash risk ÷ (stop distance in pips × pip value for 1.00 lot)

The pip value must be expressed in the account currency. For several USD-quoted major forex pairs in a USD account, one pip at 1.00 standard lot is approximately $10. Pairs with another quote currency require conversion.

EURUSD worked example

$1,000 balance · 1% risk · 100-pip stop

Cash risk: $1,000 × 1% = $10.

Cost of the stop at 1.00 lot: 100 pips × $10 = $1,000.

Position size: $10 ÷ $1,000 = 0.01 lot.

At 0.01 lot, the approximate pip value is $0.10. A 100-pip move against the position is therefore approximately $10.

XAUUSD worked example

$2,500 balance · 10% risk · 100-pip stop

Cash risk: $2,500 × 10% = $250.

Using LotSizely's XAUUSD assumption, one pip at 1.00 lot is $10. The 100-pip stop therefore costs $1,000 at 1.00 lot.

Position size: $250 ÷ $1,000 = 0.25 lot.

Under the same convention, 0.25 lot is worth $2.50 per pip and a 100-pip move is approximately $250.

Round down to the volume step

If the raw answer is 0.237 lot but the symbol accepts volume in 0.01 steps, LotSizely displays 0.23—not 0.24. Rounding down keeps the estimate at or below the target. The broker can also impose minimum and maximum volumes.

Do not force every result to 0.01 lot

If the raw size is below 0.01, the broker's minimum volume already risks more than planned. The correct response is to widen the decision—not to pretend the minimum lot fits the risk budget.

Verify in MT5 before ordering

Open Market Watch and select the symbol's Specification.
Check contract size, tick size, tick value, minimum volume and volume step.
Confirm the calculator's pip convention matches how you measured the stop.
Allow for spread, commission and possible slippage.
Review the estimated loss in the order window before submitting.

Primary reference

MetaTrader 5 documents the broker-defined contract size, tick size, tick value and volume limits in the Market Watch and Symbol Specification guide.

How to calculate lot size in MT5