Lot Size Calculator
Lot size is what your risk and your stop distance allow, not what you choose. Divide the money you will risk by your stop distance in pips times the pip value, and the answer is the size. Available leverage is a broker's ceiling, not an input.
Lots your risk allows
Defaults are a 10,000 account risking 1% with a 40-pip stop on a pair worth 10 per pip.
Lots = risk ÷ (stop in pips × pip value). Round the answer DOWN, never up — rounding up is a decision to exceed the risk you set.
Runs entirely in your browser. Nothing you type is sent anywhere or stored.
Covered on this page: TradingView.
How the number is built
Three numbers you decide, and one that falls out. The size is the one that falls out.
Lots = (account × risk %) ÷ (stop in pips × pip value)
The numerator is a decision made before the chart is open. One percent of the account, or half a percent, or whatever figure you can take twenty times in a row without changing how you behave.
The denominator comes from the chart. Where the idea is wrong, measured in pips, times what a pip is worth at a standard lot.
A worked example
Take the defaults: a 10,000 account, 1% risk, a 40-pip stop, 10 per pip.
The money at risk is 10,000 × 0.01 = 100.
The loss at the stop, per standard lot, is 40 × 10 = 400.
So the size is 100 ÷ 400 = 0.25 lots — 25,000 units, and one pip moves the position by 2.50.
Now widen the stop to 80 pips and nothing else changes. The size halves to 0.125 lots. The risk is still 100. That is the arithmetic doing the protecting — you do not have to decide to be careful, because a wider stop mechanically produces a smaller position.
Round down, always
The answer will rarely be a round number. 0.25 lots is convenient; 0.37 is not, and a broker with 0.01 granularity will let you take 0.37.
Round down to 0.37 rather than up to 0.38, and to 0.3 if your broker only does mini lots. Rounding up is a decision to carry more risk than you set, made silently and usually for tidiness.
On a small account the answer can come out below the minimum size. The honest reading of that is that the trade does not fit the account — not that the risk should rise or the stop should tighten. Tightening the stop to fit a size is the inversion this entire page argues against.
Leverage is not an input
Notice what is absent from the formula: leverage. It does not appear, because it is not a factor in how large a position should be. It is a limit on how large a position can be.
The effect of using it can be worked through. Say a holding returns 8% in a year with 20% volatility. Held at a constant 3x, simple multiplication says 24%; the standard volatility-drag approximation puts it nearer 12%, while every down day is still multiplied by three. The loss scales with the multiple and the return does not.
Which is why a size chosen from available leverage is a size chosen by the broker.
What sits on top
The spread is paid on entry regardless. A two-pip spread against a 40-pip stop is 5% of the risk gone before the position has moved, and it scales with the size the calculator returns.
And a size that is correct arithmetically can still be wrong practically. In a thin instrument or a dead session, a position the formula permits may be more than the book can absorb at the price you expect.
The original data
Of the 24,971 unique videos in the finance search study this site keeps, 14 have lot size in the title, at a median of 127,651 views across 13 channels — and 50% of those titles use explicitly calculator-shaped language. That is the highest share of calculator intent measured anywhere in the corpus. Position sizing appears in 195 titles at a median of 1,738.
Half of the lot-size searches are people asking for a calculator, at a 127,651 median — against 195 position-sizing videos at 1,738. The same arithmetic, named two ways, with a seventy-fold difference in audience. People are not searching for the concept; they are searching for the number.
The question: The stop is far away. Tighten it to trade bigger?
The answer is no, and it is the single most common way this calculation gets subverted. A stop belongs where the idea is wrong, and moving it to permit a larger position moves it to where the idea is still right — so the position is now sized correctly against a stop that will be hit by ordinary movement. The formula is intact and the input was corrupted.
When it fails
A range is where a size chosen from the account rather than the stop does the most damage. Price oscillates, stops set inside ordinary movement are touched repeatedly, and a position sized without reference to that distance loses the same amount every time rather than a scaled amount. Nothing dramatic happens — the account is ground down by a series of trades that were each the wrong size for the conditions, and the sizing rule was never actually applied.
The second failure is a gap through the stop. The planned loss was never the real one, and no sizing formula prevents that — only a smaller size does.
A third is rounding up. It is a silent decision to exceed the risk you set.
A fourth is the wrong pip value. On a yen pair the pip is 0.01, not 0.0001, and the answer is wrong by a factor of a hundred.
A fifth is forgetting the spread. It is part of what the attempt costs and it is paid on entry.
And a sixth is taking the minimum size when the answer came out below it. That is the trade not fitting the account, and the account is the thing that has to be respected.
Related
Lot size covers the unit itself and the standard, mini and micro conventions. Position sizing is the same arithmetic in every other market. And forex is where the pip value in the denominator comes from.
The order of operations is the whole thing, and it is the one people invert. Decide the risk, find where the idea is wrong, measure the distance, then let the size be whatever those three produce. Choosing a size first and then hunting for a stop that fits it is how a reasonable trade becomes an unreasonable one without anybody deciding to make it so.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money. Some links on this page earn a commission if you buy through them. It costs you nothing and it does not decide what appears here or in what order — how these pages are made is set out in our methodology.