Working out position size, instrument by instrument

Updated on September 16, 2026

One formula, one difficult term

The size calculation never changes: the amount accepted, divided by the distance to the stop multiplied by the value of one point for one lot. The first two terms are yours and easy to obtain. The third comes from the instrument, and it is the one that causes all the trouble.

That value depends on three things. The contract size, meaning what one lot represents. The quote currency, the one the price is expressed in. And your account currency, since your loss has to end up expressed in it.

If you are first trying to understand where the accepted amount comes from, and why it is the size that adjusts and never the stop, start with our page about risk per trade. This one picks up from there and deals only with moving from one instrument to another. It is also why a general-purpose assistant cannot compute a size from a screenshot. Choosing the distance itself is covered on our page about where to place your stop.

Four calculations on the same risk

Take a 5,000 dollar account, a risk of 1 %, so 50 dollars accepted on the position.

On EURUSD, one lot represents 100,000 euros, and one pip, that is 0.0001, is therefore worth 10 dollars per lot. With a 20 pip stop, the size is 50 divided by 20 times 10, so 0.25 lot.

On gold, one lot represents 100 ounces, and a one dollar move is therefore worth 100 dollars per lot. With an 8 dollar stop, the size is 50 divided by 8 times 100, so 0.0625, brought down to 0.06 lot.

On an index whose contract is worth one unit per point, each point is worth one dollar per lot. With a 120 point stop, the size is 50 divided by 120, so 0.41 lot.

On Bitcoin, one lot most often represents one bitcoin, and a one dollar move is therefore worth one dollar per lot. With a 2,000 dollar stop, the size is 50 divided by 2,000, so 0.025, brought down to 0.02 lot.

The same risk produces sizes that differ by a factor of twenty. That is normal, and it is exactly what the calculation is meant to do.

Yen pairs, and your account currency

Two situations make the point value move with the market itself.

On a pair whose quote currency is the yen, a pip is 0.01 and not 0.0001. A lot of 100,000 dollars therefore gives 1,000 yen per pip, which then has to be converted into dollars at the rate of the moment. The pip value is not fixed: it moves with the exchange rate.

The same thing affects your account. If your account is in euros and the instrument is quoted in dollars, your actual loss in euros depends on the euro-dollar rate at the time of closing. The gap is small on a short-lived position, it is not on one held for a long time.

The practical conclusion: the point value is looked up every time, on the exact symbol and at the moment of the calculation, and is never carried over from one trade to the next.

The lot step, and the floor that blocks you

Your broker does not accept any size. It imposes a step, often 0.01 lot, and a minimum volume.

Rounding is always downwards. The 0.0625 lot of the gold example becomes 0.06, which brings the risk to 48 dollars instead of 50. Rounding up to 0.07 would take it to 56 dollars, a silent breach of your own rule, on every position.

The floor is more awkward. Take Bitcoin again with a 2,000 dollar stop, on a 500 dollar account: 1 % is 5 dollars, the computed size falls to 0.0025, below the 0.01 minimum. The position is simply not takeable at that risk.

There are only three honest answers to that block. Skip the trade. Look for a setup with a shorter distance to the stop. Or use an account whose contract size is smaller, of the micro kind. Shrinking the distance to the stop to obtain a placeable size is not a solution, it is an increase in risk dressed up as a technical adjustment. Another ceiling can in fact block before that one, that of available margin.

The broker variant changes the result

The same asset can exist at your broker under two names whose contract size differs by a factor of ten. Computing on one and placing on the other gives a position ten times too big or ten times too small.

That is why the contract size has to be read on the variant actually selected, and not on the generic name. The subject is covered on our page about symbol suffixes and duplicates, and the orders of magnitude specific to each asset on those about gold and Bitcoin.

Several targets mean several orders

A plan with three targets needs three orders, sharing the same entry and the same stop. If each carries the size computed for your risk, you are not risking that amount but three times it, since they will fall together.

The size is therefore split across the targets rather than copied, which amounts to planning a staged exit from the start. That point, and how it applies to a signal you receive, are detailed on our page about risk in copy trading.

What AlphaGPT does

You set your percentage once. Every analysis and every parsed signal then read your account’s real equity, ask your broker for the contract size and point value of the exact symbol concerned, apply that broker’s lot step, and show the size directly.

When a plan carries several targets, the percentage applies to the whole and the size is split across them. And when the computed size falls below your broker’s minimum, that is said rather than rounded up to the smallest placeable size.

Trading carries a risk of capital loss.