BMI Calculator
Work out body mass index in metric or imperial units, see the WHO category, and get the healthy weight range for your height in kilograms.
Body mass index
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Enter a height and weight.
BMI is a population screening measure, not a diagnosis. It does not account for muscle, bone density or body composition, and is not valid for children, during pregnancy, or without adjustment over about 65.
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All Calculators tools →This tool runs entirely in your browser. Nothing you enter is sent to our servers, so there is nothing for us to store or see.
About the BMI Calculator
Enter a height and weight — in metric or imperial — and get the body mass index, the category it falls into, and, more usefully, the actual weight range that would be in the healthy band for that height.
That last number is the one most calculators leave out. "Your BMI is 27.4, overweight" invites the obvious follow-up question, and the answer — how many kilograms away the healthy range starts — is a single line of arithmetic that gets omitted anyway. It is shown here.
Two scales are available. The default is the WHO international one, where the healthy band runs from 18.5 to 25. The alternative uses the lower thresholds recommended for many Asian populations — 23 for overweight, 27.5 above that — because cardiometabolic risk rises at a lower BMI. That is offered as a choice rather than guessed at from anything.
BMI is a screening measure for populations, not a diagnosis for a person. It takes no account of muscle, bone density, body composition or where fat is carried, so a well-muscled athlete can read as overweight and someone with little muscle can read as healthy while carrying too much visceral fat. It is not valid for children, for pregnancy, or for people over about 65 without adjustment. Use it as one number among several.
How to use the BMI Calculator
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Choose your units
Metric takes centimetres and kilograms. Imperial takes feet and inches, and stones and pounds. Switching converts what you have already entered.
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Enter height and weight
The result updates as you type. Values well outside human range are rejected with a note about units, since that is nearly always the cause.
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Read the category and the range
The BMI figure comes with its category and, below it, the weight range that would put you in the healthy band at that height.
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Switch scale if it applies
The Asian thresholds option applies the lower boundaries recommended for many Asian populations, where risk rises at a lower BMI.
Frequently asked questions
What is a healthy BMI?
On the WHO scale, 18.5 to 24.9 is the healthy band for adults, 25 to 29.9 is overweight and 30 or above is obese. Below 18.5 is underweight. Those boundaries are population thresholds chosen where health risk starts to rise measurably, not lines between healthy and unhealthy individuals.
Why do some countries use different thresholds?
Because the relationship between BMI and health risk varies between populations. For people of South Asian, Chinese and several other Asian backgrounds, the risk of type 2 diabetes and cardiovascular disease rises at a lower BMI, so the WHO and many national health services recommend 23 rather than 25 as the point where risk increases. The tool offers that scale as an option.
Is BMI accurate for athletes?
Not usefully. BMI cannot distinguish muscle from fat, and muscle is denser, so a well-trained rugby player or weightlifter often reads as overweight or obese while carrying very little fat. If you have substantially more muscle than average, BMI is measuring the wrong thing and a body composition measure is more informative.
Can I use this for a child?
No. Children's BMI has to be read against age and sex percentile charts, because healthy body composition changes throughout growth. A fixed adult threshold applied to a child is meaningless and can be alarming for no reason. Ask a GP or use a paediatric percentile calculator instead.
Is my height and weight sent anywhere?
No. The calculation runs entirely in your browser and nothing is transmitted or stored. Height and weight are health data, which is a category most jurisdictions treat as especially sensitive — a good reason for this tool not to have a server at all.