What is a healthy BMI?

The WHO calls 18.5 to 24.9 the normal range, and 18.5 to 22.9 under the cutoffs it publishes for Asian populations. Those bands describe where population-level risk is lowest on average; they do not tell you whether any particular person at that BMI is healthy, and plenty of people outside them are.

Why does BMI say I am overweight when I am not fat?

Because it cannot tell weight apart by what the weight is made of. Muscle is denser than fat, so anyone carrying more muscle than the population average reads higher than their body composition warrants. This is well documented in athletes, and it is the single most common complaint about the measure.

Why are there different BMI cutoffs for Asian populations?

Because the relationship between BMI and cardiometabolic risk differs by ancestry. A WHO expert consultation reported in 2004 that many Asian populations show elevated risk of type 2 diabetes and cardiovascular disease at a lower BMI than European populations, and recommended additional public health action points at 23 and 27.5.

Is there a better measure than BMI?

For most purposes, waist-to-height ratio. It needs one tape measure, it captures where fat sits rather than only how much there is, and it predicts cardiometabolic risk better than BMI in most studies. A common rule of thumb is to keep your waist under half your height.

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BMI calculator

Body mass index against both the WHO scale and the WHO cutoffs for Asian populations.

Units

Weight

Height

Enter a height and weight to see your BMI.

How BMI is calculated, and what it can and cannot tell you

Body mass index is your weight in kilograms divided by the square of your height in metres. That is the whole of it — two numbers in, one number out. It carries no information about how much of your weight is muscle, how much is fat, or where on your body that fat sits, because it was never given any.

Adolphe Quetelet devised the ratio in the 1830s as a way of describing populations, not people. He was a statistician looking for the average build of a nation, and he said explicitly that it should not be used to judge an individual. It became a clinical screening tool in the 1970s largely because it is cheap: it needs a scale, a tape measure and no equipment at all.

Formulas

Metric

BMI = kg ÷ m²

Imperial

BMI = 703 × lb ÷ in²

The 703 is just the unit conversion folded into a constant.

Worked examples

Weight	Height	BMI	WHO category	Asian cutoffs
70 kg	175 cm	22.86	Normal weight	Increasing but acceptable risk
55 kg	160 cm	21.48	Normal weight	Increasing but acceptable risk
68 kg	165 cm	24.98	Normal weight	Increased risk
95 kg	180 cm	29.32	Overweight	High risk
110 kg	190 cm	30.47	Obesity class I	High risk

The 68 kg row is the point of showing both scales: normal on one, increased risk on the other.

BMI	WHO	WHO Asian cutoffs
Below 18.5	Underweight	Underweight
18.5 – 22.9	Normal weight	Increasing but acceptable risk
23.0 – 24.9	Normal weight	Increased risk
25.0 – 27.4	Overweight	Increased risk
27.5 – 29.9	Overweight	High risk
30.0 – 34.9	Obesity class I	High risk
35.0 – 39.9	Obesity class II	High risk
40.0 and above	Obesity class III	High risk

Worth knowing

BMI reads high for muscular people. Muscle is denser than fat, so a well-trained athlete can land in the "obese" band with single-digit body fat.
It reads low for people who have lost muscle with age. Two people at the same BMI, one 25 and one 75, can have very different body composition — a phenomenon sometimes called normal-weight obesity.
Where fat sits matters more than how much there is. Waist circumference and waist-to-height ratio predict cardiometabolic risk better than BMI, and neither is harder to measure.
The WHO publishes a second set of cutoffs for Asian populations, where risk rises at a lower BMI. Overweight begins at 23 rather than 25, so the two scales disagree for a large share of the world.

Frequently asked questions

What is a healthy BMI?: The WHO calls 18.5 to 24.9 the normal range, and 18.5 to 22.9 under the cutoffs it publishes for Asian populations. Those bands describe where population-level risk is lowest on average; they do not tell you whether any particular person at that BMI is healthy, and plenty of people outside them are.
Why does BMI say I am overweight when I am not fat?: Because it cannot tell weight apart by what the weight is made of. Muscle is denser than fat, so anyone carrying more muscle than the population average reads higher than their body composition warrants. This is well documented in athletes, and it is the single most common complaint about the measure.
Why are there different BMI cutoffs for Asian populations?: Because the relationship between BMI and cardiometabolic risk differs by ancestry. A WHO expert consultation reported in 2004 that many Asian populations show elevated risk of type 2 diabetes and cardiovascular disease at a lower BMI than European populations, and recommended additional public health action points at 23 and 27.5.
Is there a better measure than BMI?: For most purposes, waist-to-height ratio. It needs one tape measure, it captures where fat sits rather than only how much there is, and it predicts cardiometabolic risk better than BMI in most studies. A common rule of thumb is to keep your waist under half your height.