How to Size a Forex Position
To size a forex position, divide the amount you are willing to lose by the stop distance in pips, then divide by the pip value per unit. That gives the number of units. Leverage plays no part in the calculation; it only decides whether the resulting position is permitted.
Position sizing in forex is one division carried out twice. The reason it goes wrong is almost never the arithmetic — it is doing the steps in the wrong order, or letting the leverage the account offers stand in for a decision about risk.
Before you start
The pip value for this pair in your account currency, calculated rather than remembered. On any pair not quoted in your currency it moves with the exchange rate.
A stop distance in pips taken from the chart, before any sizing happens. The level is structural. It is not adjustable to suit a position you already want.
The currency amount you are willing to lose on this trade. A fixed percentage of the account is the standard approach, and the point is that it is decided in advance.
The steps
1. Place the stop on the chart first
Beyond the point that would prove the idea wrong. On this site’s shared series the ninetieth percentile bar range is 1.101, so a stop inside ordinary movement is not a level at all.
2. Measure the distance in pips
Entry price to stop price, converted to pips using the correct decimal for the pair. Four decimals on most, two on yen pairs.
3. Calculate the pip value for this pair today
One pip times one unit, converted to your account currency. On a pair quoted in your currency this is constant; on anything else it is today’s number.
4. Divide risk by pips, then by pip value
Risk amount divided by stop pips gives the money per pip you can afford. Divided by the pip value per unit, it gives the number of units. Convert to lots last.
5. Check the result against the account, not the leverage
Leverage tells you the position is allowed. Whether one adverse move should be able to remove a large part of the account is a separate question the broker does not ask.
6. Round down, never up
0.37 lots becomes 0.3. Rounding to 0.4 is a small number and it is a deliberate breach of the figure you set, repeated on every trade.
7. Redo the arithmetic if the stop moves
Widening the stop without reducing the size increases the risk proportionally. The two numbers are linked, and changing one alone is changing the amount at risk without deciding to.
How to tell it worked
The stop was placed before the size was calculated, in that order every time.
The pip value was recalculated within the last 1 day on any converted pair.
The result was rounded down, so the actual risk is at or below your figure.
And 1 adverse move to the stop costs the amount you decided, checked in currency rather than assumed.
Why leverage is not in the formula
Leverage decides how much margin the position ties up. It does not change the distance to your stop or what a pip is worth, which are the only two things the loss depends on.
A high-leverage account with a correct position size behaves identically to a low-leverage one. The leverage only becomes visible when the size was chosen by what the account permitted rather than by this calculation.
A worked example
Risk 100 of your account currency. Stop 40 pips. Pip value 0.0001 per unit, no conversion needed.
100 divided by 40 is 2.50 per pip. That is what one pip of movement can be worth without exceeding the limit.
2.50 divided by 0.0001 is 25,000 units, which is 0.25 standard lots. Round down if the broker’s increments require it.
Change the stop to 80 pips and the size halves to 12,500 units. The risk is unchanged at 100, which is the whole point of doing it in this order.
Where the risk figure itself comes from
A fixed percentage of the current account balance is the standard answer, and the reason it is standard is that it shrinks the position automatically during a losing run.
Recalculating it from the current balance rather than the starting one is what makes that work. A percentage of a number set six months ago is a fixed amount wearing a percentage’s clothing.
The size of the percentage is a judgement, and the arithmetic behind it is not. On this site’s shared series 95% of bars sat below a prior peak and the longest recovery took 73 bars, so a sequence of losses is the ordinary condition rather than an unusual one.
What matters most is that the figure exists before the trade. A risk amount chosen while looking at a setup is chosen by how good the setup looks, which is the opposite of a limit.
The original data
Of the 24,971 unique videos in research/search-study-corpus.jsonl, 34 cover position sizing in the
title, at a median of 2,037 views across 32 channels, and 50% of those are instruction-shaped. Forex
generally appears in 1,323 at 10,190 and pips in 27 at 13,840. The counts come from
site/corpus_count.py and site/rank_howto.py.
34 videos at 2,037 against 1,323 forex videos at 10,190. The arithmetic that decides how much any of those strategies can lose has a fortieth of the coverage and a fifth of the audience per video.
The answer to the question on that chart is that a smaller size at the correct stop is the same risk. The trade is not worse for needing a wide stop; it is smaller. Skipping it because the size looks trivial is deciding by position size rather than by the setup, which is the same error running in the other direction.
When it fails
The failure is sizing first and placing the stop afterwards, and it produces stops that look arbitrary because they are. A position size gets chosen — often from what the account permits — and the stop is then placed wherever it makes the loss acceptable. That level has nothing to do with the chart, so it sits inside ordinary movement, and the trade gets stopped out by nothing in particular before the idea has had a chance to be right or wrong.
The second failure is a stale pip value. Actual risk drifts from intended.
A third is rounding up. A small breach, repeated every trade.
A fourth is the wrong decimal on a yen pair. The size is out by a hundred.
A fifth is treating leverage as a sizing input. It sets what is allowed.
And a sixth is widening a stop without resizing. The risk rises with the distance.
Related
Position sizing covers the principle across all instruments. Lot size is the unit the answer converts into. And risk per trade is where the currency amount comes from.
What fixed this for me was doing the three steps in a fixed order and never varying it: stop first, then pip value, then size. When I did it the other way round — decided the lots, then found a stop that suited them — the stop was always in a place the market could reach for no particular reason.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.