BMI Calculator
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A BMI calculator in metric or imperial, worked out in your browser.
- Choose metric or imperial
- Enter your weight and height
- Your BMI, its range, and the healthy weight span for your height appear as you type
BMI is a rough guide, not a diagnosis. It cannot tell muscle from fat, and is read differently for children, during pregnancy, and across ethnic groups.
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About this tool
Body mass index is your weight divided by the square of your height, and that really is the whole formula. It was devised in the 1830s to describe populations rather than individuals, which is worth knowing before reading much into your own number: BMI cannot tell muscle from fat, so it classes a great many athletes as obese, and it is interpreted differently for children, during pregnancy, and across ethnic groups. What it is reasonably good at is being a quick first look — which is why this shows the healthy weight range for your height alongside the number, because "the healthy range for 175 cm is 57 to 77 kg" is something you can act on where a one-word category is not. Enter your measurements in whichever system you think in; kilograms and centimetres or pounds and feet both work, and the conversions use the exact defined values rather than rounded ones so the two agree to the decimal. Everything is calculated in your browser, so nothing about your body is transmitted, logged, or stored anywhere.
Frequently asked questions
What is a healthy BMI?
The World Health Organization puts the healthy adult range at 18.5 to 25. Below 18.5 is classed underweight, 25 to 30 overweight, and 30 or above obese. Those boundaries are conventions rather than cliffs — 24.9 and 25.1 are not meaningfully different, whatever the label changing suggests.
How do I calculate BMI?
Weight in kilograms divided by height in metres squared — but you do not have to: type either metric or imperial and it converts. As a bmi calculator kg and cm are the default because that is the formula's own units, and the imperial version multiplies by 703 to reach the same number.
How is BMI calculated?
Weight in kilograms divided by height in metres squared. So 70 kg at 1.75 m is 70 ÷ (1.75 × 1.75), which is 22.9. In pounds and inches the formula is weight ÷ height² × 703, which is the same sum with the unit conversion folded in.
Is BMI accurate for everyone?
No, and it is worth being clear about that. It measures neither body fat nor where fat sits, so muscular people are routinely classed overweight or obese while being nothing of the sort. It is also read differently for children, pregnant women, older adults and across ethnic groups. Treat it as one rough indicator among several rather than an assessment of your health.
Why show a healthy weight range?
Because it is the part you can do something with. A category tells you which side of a line you are on; the range tells you what the line actually is in kilograms or pounds for someone your height, which is a far more useful thing to know.
Is my weight sent anywhere?
No. The calculation happens in your browser and nothing leaves it — no server sees your height or weight, and nothing is stored. You can disconnect from the internet after the page loads and it keeps working.
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