Work out your body mass index and see it against the WHO, WHO Asia-Pacific and Taiwanese thresholds — which classify the same number differently.

The formula

BMI = weight in kilograms ÷ (height in metres)²

That is the whole calculation. Someone 1.70 m and 69 kg has a BMI of 23.9.

The same number, three answers

This is the part most calculators leave out. There is no single set of thresholds, because the relationship between BMI and metabolic risk differs between populations:

	Overweight from	Obese from
WHO international	25	30
WHO Asia-Pacific	23	25
Taiwan (HPA)	24	27

A BMI of 23.9 is a healthy weight internationally, overweight under the Asia-Pacific cut-offs, and just inside healthy in Taiwan. All three are official; they are answering the same question about different populations.

The reason is body composition. At the same BMI, people of East and South Asian descent tend to carry more body fat and more visceral fat than people of European descent, and develop type 2 diabetes and cardiovascular disease at lower BMI values. The WHO’s 2004 expert consultation recommended lower action points for Asian populations for exactly this reason. Taiwan’s Health Promotion Administration sets its own at 24 and 27; Hong Kong’s Department of Health follows the WHO Asia-Pacific figures.

If you are in Taiwan or Hong Kong and a calculator tells you 24 is fine, it is applying thresholds that were not written for you.

Full bands

Taiwan (HPA)

BMI	Band
under 18.5	Underweight
18.5 – 23.9	Healthy weight
24 – 26.9	Overweight
27 – 29.9	Obese, class I
30 – 34.9	Obese, class II
35 and over	Obese, class III

WHO international

BMI	Band
under 18.5	Underweight
18.5 – 24.9	Healthy weight
25 – 29.9	Overweight
30 – 34.9	Obese, class I
35 – 39.9	Obese, class II
40 and over	Obese, class III

What BMI does not measure

BMI was devised by Adolphe Quetelet in the 1830s as a way of describing populations. It was never intended to diagnose an individual, and it cannot, because it has only two numbers to work with:

It cannot tell muscle from fat. A trained athlete and a sedentary person of the same height and weight have the same BMI and very different health.
It cannot see where the fat is. Visceral fat around the organs carries far more risk than the same mass on hips and thighs. Waist circumference and waist-to-height ratio capture this and BMI does not.
It scales wrongly with height. Squaring the height under-corrects, so BMI reads slightly high for tall people and slightly low for short ones.

A widely used rule of thumb that BMI misses entirely: keep your waist under half your height. It needs one tape measure and no calculator, and it predicts metabolic risk better than BMI does.

Where it does not apply at all

	Use instead
Children and teenagers	age-and-sex BMI percentiles — a child’s healthy BMI changes every year
Pregnancy	pre-pregnancy BMI, with weight gain tracked separately
Athletes and heavy training	body composition measurement
Older adults	slightly higher ranges are often appropriate
Amputees, and some conditions	BMI is not meaningful

What the healthy range means

The range shown is simply the weights that would put your height inside the healthy band under the selected standard. At 1.70 m that is 53.5–69.4 kg under Taiwan’s thresholds, and 53.5–72.3 kg under the WHO’s. The lower bound is 18.5 in every standard; only the top moves.

This is a screening figure, not a diagnosis

BMI is useful for one thing: a cheap, fast signal that a conversation might be worth having. Nothing on this page is medical advice, and a number outside a band is a reason to ask someone qualified rather than a conclusion.

Everything is calculated in your browser. No height, weight or result is sent anywhere.

BMI calculator