Position Size by Instrument: Contract Size, Pip Size and Unit Step

Take one account of 10,000 USD, one budget of 1% (100.00 USD), and put the same trade idea on seven different instruments. Every one of them loses exactly 100.00 USD if its stop is hit — and every one of them needs a completely different order size to do it:

Nothing about the setup changed. Only three numbers per instrument changed, and those three numbers are why a size that is conservative on one symbol is reckless on another.

The three numbers that decide your size

Contract size is how many units sit inside one lot. It is 100,000 for a forex pair, 100 for XAU/USD, 5,000 for XAG/USD, 1,000 for WTI/USD, and 1 for most indices and crypto pairs. Lots are a display convention; losses are paid per unit, so the contract size is what converts a number you can compare across platforms into a number your broker will accept.

Pip size is the price increment the instrument quotes in, and it is not 0.0001 everywhere. Every JPY pair uses 0.01. Silver uses 0.001. An index quotes whole points, so its pip size is 1. Get this wrong and a "20 pip stop" is twenty of something completely different on another symbol.

Unit step is the smallest increment your broker accepts. Forex pairs will usually take 1,000 units (0.01 lots); gold and indices step in whole units; crypto steps in fractions (0.001 BTC is common). The step is the reason a computed size that is not a multiple of it has to be rounded down — rounding up spends risk you did not budget.

Why the same percentage produces wildly different position values

Look again at the table above: EUR/USD puts 55,000 USD of notional behind a 100.00 USD risk, while gold puts 120,000 USD behind the same 100.00 USD. Neither trade is bigger than the other in risk terms. They differ because the gold trade's stop is 2.00 dollars wide on a 2,400 dollar price — 0.08% of the price — while the EUR/USD stop is 0.0020 wide on 1.1000, roughly 0.18% of the price.

The consequence is the part that surprises people: a tight stop in price terms buys you more units, and more units mean more notional. If you size by looking at the position value and thinking "that is too much exposure", you will cut the trades that are actually correctly sized, and keep the ones that are not.

The right order is always: fix the stop first for the chart, convert it to a distance, pay the budget against that distance, then look at the resulting notional and ask whether margin and exposure limits still allow it.

Specifications by asset class

A representative slice from the 131 instruments in our reference table. Quote currency matters twice: it sets what your loss is denominated in, and it decides whether a conversion rate is needed to express it in your account currency.

The 131 rows break down as 67 forex pairs, 43 crypto pairs, 12 indices, 4 metals, 3 energies, plus a stock row and a custom row you can point at any unlisted instrument.

The four mistakes this table kills

• Assuming 100,000 everywhere. One lot is 100 oz of the same size contract that gives 5,000 oz of silver. Sizing "one lot" on silver because one lot is normal on EUR/USD multiplies the risk by fifty.
• Using 0.0001 as the pip for every pair. On USD/JPY a 0.20 move is 20 pips, not 2,000. Sizing tools that hardcode 0.0001 produce sizes that are off by a factor of one hundred on every JPY cross.
• Ignoring the unit step. A computed size of 17,400 units is not sendable on a 1,000-unit step instrument; 17,000 is. The 400 units you drop also drop a little of your risk, which is the right direction to err.
• Forgetting the quote currency. A loss priced in JPY or CAD is not a loss in USD until it is converted. Skip the conversion and every size on a cross pair is wrong by whatever the rate happens to be that day.

Checklist before you send the order

• Confirm the stop in price terms for the chart first; do not pick a size and then invent a stop that fits it.
• Check the instrument's pip size so the stop distance means what you think it means.
• Pay the budget against the distance, then round down to the unit step.
• Convert the result into lots with the contract size, so it matches what your order ticket asks for.
• Only then check the notional against your exposure limit and your margin.
• Verify the three numbers against your broker's own specification sheet — ours is what the tool assumes, not what every broker deals.

Open the position size calculator

Related guides

• How to calculate position size in forex — the single-instrument version of the same formula.
• Reference data — contract size, pip size and unit step for all 131 instruments.
• Forex profit calculator — what the spread and commission do to a result once the size is fixed.
• Adding to a position — splitting one budget across several entries.