BMI and Waist-to-Height Calculator
Body mass index with the WHO band it falls in, and the waist-to-height ratio that covers what BMI misses.
Runs entirely in your browser. Nothing is uploaded, logged or stored.
Body mass index
22.9
- WHO band
- Normal range (18.5 to 24.9)
- What the WHO normal band is at this height
- 56.7 – 76.3 kg
- Against the 2004 Asian-population action points
- below all of them (23, 27.5, 32.5, 37.5)
Body mass index is weight divided by height squared. That is all it is, and this page shows it with the band the World Health Organization places it in — named as theirs, not as a judgement this page is making.
Beside it is the waist-to-height ratio, because it answers what BMI cannot: where the weight is. NICE recommends measuring both, and says the ratio holds for all ethnicities, both sexes and adults with high muscle mass — the group BMI classifies wrongly.
How it works
BMI was devised by Adolphe Quetelet in the 1830s as a way of describing **populations**, and he said so. Ancel Keys, who gave it the name in 1972, said the same: it is a screening measure for groups, adapted to individuals afterwards and imperfectly. It cannot distinguish muscle from fat, it says nothing about where the weight sits, and a well-trained athlete routinely lands in the pre-obese band.
The waist-to-height ratio needs a tape measure and answers a different question. NICE places it in three bands — 0.4 to 0.49 healthy, 0.5 to 0.59 increased, 0.6 or more high — and the rule worth remembering is simply to keep your waist under half your height. Above a BMI of 35 NICE says the ratio adds nothing, so the page stops offering it there.
The 2004 WHO consultation on Asian populations is reported as it actually concluded, which is not what most pages claim. It identified additional public-health action points at 23.0, 27.5, 32.5 and 37.5, and it **retained the international classification** rather than redefining it. The observed-risk threshold varies from 22 to 25 between Asian populations, which is precisely why no single second set of categories was created.
Under eighteen this page refuses. Children and adolescents are assessed against age- and sex-specific growth references, and a fixed adult threshold applied to a fourteen-year-old is not a rough answer — it is the wrong instrument.
Examples
| Case | Input | Result |
|---|---|---|
| An ordinary reading | 70 kg, 175 cm | BMI 22.9 — WHO normal range |
| Where BMI gets it wrong | 95 kg, 180 cm, waist 84 cm | BMI 29.3 (pre-obese), waist ratio 0.47 (healthy) |
| The rule worth remembering | height 175 cm | keep the waist under 87.5 cm |
Frequently asked questions
I am muscular and it says I am overweight. Is it wrong?
About you, very possibly. BMI counts kilograms and cannot ask what they are made of, so muscle reads exactly like fat. This is the single best-known limitation of the measure and it is why the waist-to-height ratio is on this page: NICE states that ratio applies to adults with high muscle mass, and BMI does not.
Are the bands different for Asian populations?
Not in the way most pages claim. The 2004 WHO consultation identified extra public-health action points at 23.0, 27.5, 32.5 and 37.5, because the proportion of Asian people at high risk is substantial below a BMI of 25. But it explicitly kept the international classification and did not redefine the categories — the risk threshold varies from 22 to 25 between Asian populations, so no single replacement was possible. This page reports the action points as what they are.
Why does it refuse under eighteen?
Because the answer would be meaningless. A growing body is compared against age- and sex-specific percentile charts, not against fixed numbers — a BMI of 19 means something entirely different at ten than at forty. A doctor or a school nurse has the right charts.
Where do I measure the waist?
Halfway between the bottom of the lowest rib and the top of the hip bone, standing, breathing out, with the tape snug but not pulled tight. Not at the trouser line, which is lower and gives a smaller number.
Why is there no "ideal weight" here?
Because the formulas those calculators use do not support the claim. Broca's and Lorentz's are rules of thumb with nothing behind them, and Devine's was devised for calculating drug doses rather than for health. What this page shows instead is the weight range the WHO normal band covers at your height, which is a range and not a target.
Is BMI useless, then?
No — it is useful for what it was built for. Across a population it tracks health risk well and costs nothing to collect, which is why public health uses it. The error is reading a population instrument as a verdict on one person, and the two measurements together say more than either alone.
Good to know
- Nothing here is medical advice, and nothing you type leaves the page. The arithmetic runs in your browser and the form never submits, so no measurement reaches a server log, a referrer header or the address bar — which is also why there is no share link.
- BMI is meaningless during pregnancy, and it is a poor guide for anyone with a large amount of muscle, for older people who have lost muscle, and for anyone with a limb difference. The waist ratio helps with the second of those and not with the others.
Sources
- World Health Organization — Body mass index classification
- WHO expert consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet 363 (2004), 157–163
- NICE NG246 — Identifying and assessing overweight, obesity and central adiposity