BMI calculator — your body mass index, and the healthy weight range for your height

Body mass index is weight in kilograms divided by height in metres squared. The formula goes back to the 1830s, when the Belgian statistician Adolphe Quetelet was looking for a simple way to describe how the build of a population is distributed — he was studying groups of people, not patients, and he never proposed it as a measure of an individual’s health. It was picked up as a screening tool much later, in the second half of the twentieth century, and the name "body mass index" belongs to that period rather than to Quetelet. That origin explains both its strength and its weakness in one line: it is a population statistic that people now use one person at a time.

Kilograms divided by metres squared, and nothing else. If you enter feet, inches and pounds, those are converted to metres and kilograms first — this page does not use the 703 shortcut you see elsewhere, because 703 is a rounded version of the real conversion factor (703.0696…) and it quietly makes the imperial answer disagree with the metric one in the last digit. The WHO bands for adults are: below 18.5 underweight, 18.5 to 24.9 normal, 25.0 to 29.9 overweight, 30.0 to 34.9 obese class I, 35.0 to 39.9 obese class II, and 40.0 or above obese class III. Because those bands are written to one decimal, this calculator rounds your index to one decimal first and then classifies the rounded figure — so a result that displays as 25.0 is always labelled overweight, and never sits next to the word "normal" because the unrounded value happened to be 24.97.

Because it is cheap, fast and reproducible, and nothing better shares those three properties. It needs a tape measure and a set of scales, it takes under a minute, two people measuring the same person get the same answer, and it can be collected from millions of people and compared across decades and across countries. Methods that measure body composition directly — DEXA scans, hydrostatic weighing, air displacement — are far more accurate about what your body is made of and are far too slow and expensive to run at population scale. So BMI survives as a screening threshold: a way of deciding who might be worth looking at more closely. It was never meant to be the last measurement anybody takes, and that is the distinction that gets lost when it appears on a personal report as though it were a verdict.

No, and this is its most-quoted flaw for a good reason. The calculation sees one weight figure; it has no way to know what that weight is made of. Muscle is denser than fat, so a well-trained athlete or a heavy manual worker can land in the overweight band, or even the obese band, while carrying very little fat — for them the number means nothing at all. The reverse is just as real and gets far less attention: somebody with little muscle can sit comfortably inside the normal band while carrying a lot of fat, and a normal BMI can therefore be falsely reassuring. BMI also says nothing about where the weight sits, and waist measurement is the usual companion for that reason. If either of those descriptions sounds like you, the number on this page is not the measurement you should be relying on.

No to all three, and this calculator deliberately does not offer a child mode. Children and teenagers are still growing, and their healthy body composition changes month by month, so paediatric BMI is not read against fixed thresholds at all — it is plotted on percentile charts specific to age and sex, and only a clinician using the right chart for that child can interpret it. During pregnancy, weight gain is expected and the index has no useful meaning; a pre-pregnancy figure is what maternity care normally works from. In older adults it drifts in two directions at once: height is lost as the spine compresses, which pushes the index up on paper without any change in the body, while muscle is lost with age, which means the same index can hide a very different body composition. Building a child mode here would mean printing a fixed threshold where a chart belongs, which would be worse than not offering the feature.

It does not, and the standard cut-offs on this page come with a widely-noted caveat. The World Health Organization has itself observed that for many Asian populations the risk of conditions like type 2 diabetes and cardiovascular disease begins rising at a lower BMI than the international thresholds suggest, and a number of health authorities have adopted lower action points as a result — a figure in the region of 23 rather than 25 is the one usually discussed for overweight. We are not printing a specific national guideline number on this page and not attributing one to any particular body: those figures differ between countries, are revised, and a number copied into a web page and left there is exactly the kind of thing that looks authoritative while being out of date. The honest version is the general point. This is a Malaysian site and a great many of our visitors are in exactly the group that caveat is about, so if you are in the upper part of the normal band, treat that as a reason to ask a doctor rather than as a clean bill of health. Body composition at a given BMI also varies with sex, age and ethnicity more broadly, which is a further reason the index is a screen and not an answer.

Because there is no such thing as a single ideal weight, and printing one would be inventing precision the method does not have. The normal band spans BMI 18.5 to 24.9, which for an adult of 1.70 m works out to roughly 53.5 kg to 71.9 kg — a spread of nearly twenty kilograms, all of it equally "normal" by this measure. Which part of that range suits a particular person depends on build, muscle, age and history, none of which the formula knows anything about. A range is also the more useful thing to know in practice: it tells you whether you are inside or outside the band and by how much, without implying that one number in the middle is a goal you have missed. The reference table further down this page gives the same range for a series of heights, computed by the same code that runs the calculator, so the two can never disagree.

No. The calculation is JavaScript running in this tab, there is no server involved at any point, and the page works with the connection off once it has loaded. Your height and weight are not sent anywhere, and unlike some tools on this site this page writes nothing to your browser’s local storage either — the answer takes one sitting, and height and weight are personal enough that keeping them buys nothing. Close the tab and the numbers are gone. The page itself carries advertising, which is a third-party request made when the page loads and is explained in full on our privacy page.