Position sizing is the decision of how large a trade should be, given the account and the distance to a planned exit. It is not a measure of confidence, and it is not a way to make a small account feel large. It is the arithmetic that turns “I can accept this loss” into a number of lots, shares or contracts.
Many beginners reverse the order. They choose a size that looks meaningful in pounds, then hope the market stays close to the entry. That is how a normal swing in GBP/USD during London becomes an outsized result.
Risk First, Size Second
A practical sequence is to decide how much of the account a single idea is allowed to cost if it is wrong, then work backwards. The stop distance, in pips or points, is an input. Size is the output.
If you are prepared to risk £20 on a GBP/USD idea, and the invalidation is 40 pips away, the position has to be small enough that a 40-pip move costs about £20. If the same £20 budget meets an 80-point stop on a FTSE contract, the size will be different again. The risk target stayed still. The instrument did not.
The Percentage People Repeat
You will often hear a figure in the region of 0.5% to 1% of the account per trade. On a £2,000 balance, 1% is £20. On a £10,000 balance it is £100. The percentage is a ceiling some traders use, not a target to spend.
There is nothing magic about 1%. It is a way of surviving a cluster of losses. Five losing trades at 1% is not the same event as five losing trades at 5%. The second sequence can end the learning period before the method has had a chance to show whether it has any merit.
A higher percentage does not make a better idea. It only makes the idea louder.
How Size Follows the Stop
Once the cash risk and the stop distance are known, size is a calculation. Pip value, or point value, is the bridge.
Suppose the planned exit on cable is 25 pips from the fill, and the cash risk is £15. You need a size whose 25-pip move is worth about £15. If that size feels “too small to bother with”, the issue is usually the account, or the expectation, not the formula.
Copying someone else’s lot size is unwise. Their stop, their balance and their tolerance are not yours. A 0.10 lot on GBP/USD can be conservative on one account and reckless on another.
If that order of operations is still fuzzy, a free traders assessment can help you see whether you currently pick size before risk, or the other way round.
Why “Small Size” Still Goes Wrong
Size can be modest on paper and still too large in practice. Correlation is one reason. Three sterling pairs that all move with the dollar are not three independent 1% risks. They can behave like one larger bet.
Another reason is changing size after a result. Increasing the next ticket to recover a loss turns position sizing into a mood.
Costs matter too. A size that looks correct before the spread can be slightly too large after it. Daily loss limits sit above the single-trade figure. One correctly sized trade does not grant a free afternoon of repeats.
Keeping the Number Honest
A compact way to keep sizing from drifting is to write the steps down before the session, not during it.
- State the account risk in pounds, as a small fraction of capital
- Measure the stop from structure, not from a round number chosen for comfort
- Convert that distance into size using pip or point value
- Check whether other open trades are really the same idea in disguise
- Leave the size alone after the fill, unless the original plan said otherwise
For teaching that puts this arithmetic ahead of chart patterns, Samuel and Co Trading offers structured courses for people who want risk to be a number, not a feeling.
If you want to test how you currently choose size, take a free traders assessment and treat the result as a study prompt.
Conclusion
Position sizing answers how much to risk per trade by starting with an acceptable cash loss, then fitting the ticket to the stop. Percentages in the region of 0.5% to 1% are a common ceiling, not a promise.
The market will not reward a larger size because the idea felt strong. It will only magnify the outcome. Get the pounds right first, and the lot size usually follows.
