BMI
Body mass index, your healthy weight range in real units, and the WHO cut-offs for Asian populations that most calculators leave out.
24.2
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- Healthy weight range
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- To the healthy range
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- BMI Prime
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- Ponderal index
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- Waist-to-height ratio
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BMI is a screen for populations, not a measurement of you. It cannot tell muscle from fat, nor where the fat sits — the two things that actually carry the risk.
How BMI is calculated
Metric, it is weight in kilograms divided by height in metres squared. Imperial, it is 703 × weight in pounds ÷ height in inches squared — the 703 exists only to make the imperial answer match the metric one. Same formula for men and women: BMI has no sex term, so "BMI calculator for women" and "BMI calculator for men" return the same number for the same body.
What your category means, and what it does not
The WHO bands — under 18.5, 18.5 to 24.9, 25 to 29.9, 30 and over — are drawn from population mortality data. They describe how risk shifts across a large group. They do not describe you, and a number one point either side of a boundary is not a meaningfully different body.
The index has one well-known failure in each direction. A lifter with a lot of lean mass reads as overweight or obese while carrying very little fat. An older adult who has lost muscle can read as a healthy weight while carrying a great deal. Both are the same flaw: BMI only knows your total mass.
Why the thresholds are lower for Asian populations
At the same BMI, people of South Asian, Chinese and South-East Asian descent tend to carry more body fat and more of it around the organs, and develop type 2 diabetes and cardiovascular disease at lower body weights. The WHO's 2004 expert consultation therefore set public-health action points at 23 and27.5 rather than 25 and 30. NICE carries the same adjustment in UK guidance.
Switch the cut-offs above and the bands move; the arithmetic does not. If your background sits across more than one of these groups, read both.
Waist-to-height ratio often tells you more
Where fat sits matters more than how much you weigh, and a tape measure is better at finding that than a set of scales. NICE now recommends keeping your waist to less than half your height alongside BMI, for anyone with a BMI under 35. Enter a waist measurement above and this page will work it out, or use thewaist-to-height calculator for the full bands.
Where BMI should not be used at all
It is not valid during pregnancy or while breastfeeding. For anyone under 20 it has to be read as a percentile against age and sex, which needs growth reference data this page does not carry — ask a GP rather than reading an adult category. And it is a screening number, not a diagnosis: a result outside the healthy band is a reason to have a conversation, not a verdict.
Turning this into a plan
If you have decided to lose weight, the useful next number is not your BMI but your maintenance intake. Themaintenance calculator gives you that, and the deficit calculator turns it into a daily target and a date.