Position sizing — calculate units for a stated loss budget

Consider a hypothetical $2,500 EUR/USD account trading one standard lot. A 30-pip adverse move represents $300 before costs, or 12 percent of starting equity. The order window’s default is not a risk budget. This article shows how to convert a planned risk allowance, stop distance and pip value into an appropriate permitted volume.

Part 1 of 5A chosen percentage budget

For the exercises, choose 1% of a stated capital base as the planned price-loss budget. On 10,000 USD that is 100 USD. The percentage is a model input, not a universally appropriate rule or a guarantee of the final loss. State whether the base is balance or current equity, and assess other positions separately.

Assume each of ten consecutive losses is exactly a fixed fraction of capital remaining after the previous loss, with no cash flows or extra charges. At 1%, capital is 0.99¹⁰ ≈ 90.438% of its start, a 9.562% drawdown. At 5%, it is 0.95¹⁰ ≈ 59.874%, down 40.126%; at 10%, 0.90¹⁰ ≈34.868%, down 65.132%. Recovery to the initial amount needs about 10.573%,67.018% and 186.797% on the remaining capital respectively. These are hypothetical sequences, not forecasts of a losing streak or a recovery run.

Part 2 of 5Lots and pip value — what one move actually costs

First establish the instrument’s units. In the standard FX convention, one lot is 100,000 base-currency units, a mini-lot 0.10 is 10,000 and a micro-lot 0.01 is 1,000. A nano label does not establish availability. The symbol may use another contract size, minimum or volume step; check these before using the three basic lot sizes in a budget calculation.

In the hypothetical linear EUR/USD model, contract size is 100,000 EUR per lot and the pip is 0.0001 USD/EUR, giving 10 USD per pip per lot before separate costs. For a pair quoted in JPY, such as USD/JPY, a common pip convention is 0.01 JPY per base unit:100,000 USD then gives 1,000 JPY per pip. At a separately assumed reference conversion of 150 JPY/USD, that is 6.6667 USD. Reversed quotations and other products require their own specifications. See pip values for individual pairs.

Part 3 of 5The position-size formula

The simple price-loss model uses three inputs; separate costs and order constraints require additional checks:

1. Chosen capital base × chosen fraction — the planned price-loss budget in account currency; here the fraction is 1%.
2. Stop-loss distance in pips — the distance from your entry to the level at which your idea stops being valid.
3. The value of one pip on one lot for that specific pair, converted into your account currency.

In this simple model, lots = chosen price-loss budget / (stop distance in pips × pip value per lot). Keep units and conversion consistent, then round a calculated ceiling down to the permitted step and check the minimum. For example, the Polish cost extension assumes a 100 USD total budget,30-pip distance,10 USD/pip/lot, a 10 USD fixed cost and 6 USD/lot variable cost:300 q +6 q +10 ≤100 gives q ≤90/306 ≈0.29412, or 0.29 at a 0.01 step. That gives 98.74 USD, while 0.30 gives 101.80. The model assumes its stated fills and fees; worse execution or later charges can exceed the budget. For volume units, see the lot entry in the forex-basics.com glossary.

Part 4 of 5Three conversions: a dollar account, a euro account and a yen pair

With a 100,000-EUR contract and the stated 30-pip exact fill distance,0.33 lot gives 99 USD of price loss before separate costs. In a standalone hypothetical margin model using notional /30,33,000 EUR requires 1,100 EUR margin, or 1,235.74 USD at the example’s 1.1234 conversion. Historical ESMA 2018 intervention and current national retail CFD rules are separate contexts; actual category, provider, client status and margin method govern. Margin does not cap the loss.

For a separate hypothetical EUR-account exercise, capital 10,000 EUR and a chosen 1% budget give 100 EUR. Keep reference conversion fixed at 1.0800 USD/EUR and costs zero. One-lot pip value is 10/1.08 EUR; using full precision,100 / (30 ×10/1.08) =0.36 lot exactly. Its estimated thirty-pip price loss is 100 EUR under that fixed conversion. A real closing conversion can differ; this is not a maximum-loss guarantee.

For a separate USD/JPY exercise, assume 100,000 USD per lot, a 0.01 JPY/USD pip and fixed reference conversion 150 JPY/USD. One-lot pip value is 1,000/150 USD. A 100 USD price budget over 40 pips gives 0.375 lot before rounding, or 0.37 at a 0.01 step, with estimated loss 98.6667 USD. Retain full precision rather than size from a rounded 6.67. The actual exit conversion, costs and stop fill can change the final amount.

Part 5 of 5What to do tomorrow

1. Check the minimum tradable size. Find the instrument’s minimum volume and step. If the minimum exceeds your risk allowance at the planned stop, skip that trade or consider a suitable specification in a demo environment. A sizing constraint is not a reason to raise the risk percentage or deposit more money.
2. Record pip value with its assumptions. Keep contract size, pip convention, account currency and conversion beside standard/mini/micro estimates. Refresh them when inputs change; memorising a number does not make it a stable specification.
3. Compare planned and realised loss. Record the capital base, chosen fraction, requested stop, executed units, actual exit and costs for each sample trade. A stop-distance estimate is not the realised result. Evaluate departures from the stated plan, rather than call every allocation above 1% a mistake. The wider mechanics appear in the basics of risk management.