BMI, or body mass index, is your weight in kilograms divided by the square of your height in metres. It is a screening measure that sorts adults into weight categories, not a measure of health or body composition.

How do I calculate BMI?

Divide your weight in kilograms by your height in metres squared. In imperial units, multiply your weight in pounds by 703, then divide by your height in inches squared. Both give the same result.

What is a healthy BMI?

For adults, the World Health Organization defines 18.5 to 24.9 as the healthy range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classified as obesity.

Is BMI different for men and women?

No. Adult BMI uses the same formula and the same category thresholds for both. What differs is body composition: at an identical BMI, women typically carry a higher body fat percentage than men.

Why is BMI considered inaccurate?

BMI uses only height and weight, so it cannot tell muscle from fat or show where fat is stored. It commonly misclassifies muscular people as overweight, and it can miss excess body fat in people whose weight looks normal.

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Your BMI, and what it actually means

Body mass index (BMI) is your weight in kilograms divided by the square of your height in metres. It sorts adults into four broad categories — underweight, healthy weight, overweight and obesity — using thresholds that are identical for men and women.

It is a fast screening measure, not a diagnosis. It cannot tell muscle from fat, and it cannot see where fat is stored. Most calculators stop at the number; this one tells you where it holds up and where it breaks down.

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Calculate your BMI

Enter your height and weight. Nothing is sent anywhere — the calculation runs entirely in your browser.

Live calculation needs JavaScript. You can still work out your BMI from the formula and the reference chart further down this page — find your height row and compare your weight to the ranges shown.

Where your number sits

The BMI scale

The categories are bands on a continuum, not steps. A BMI of 24.9 and one of 25.1 are practically identical bodies on opposite sides of a line drawn for convenience.

Underweight
Healthy weight
Overweight
Obesity, class I
Obesity, class II

Calculate above and your position appears on the scale.

BMI chart by height and weight

Weight in kilograms at each BMI threshold. Find your height, then see which range your weight falls into.

BMI chart by height and weight
Height	Underweight under	Healthy 18.5–24.9	Overweight 25–29.9	Obesity 30+
155 cm	under 44 kg	44–60 kg	60–72 kg	72 kg and above
160 cm	under 47 kg	47–64 kg	64–77 kg	77 kg and above
165 cm	under 50 kg	50–68 kg	68–81 kg	82 kg and above
170 cm	under 53 kg	53–72 kg	72–86 kg	87 kg and above
175 cm	under 57 kg	57–76 kg	77–92 kg	92 kg and above
180 cm	under 60 kg	60–81 kg	81–97 kg	97 kg and above
185 cm	under 63 kg	63–85 kg	86–102 kg	103 kg and above
190 cm	under 67 kg	67–90 kg	90–108 kg	108 kg and above

BMI categories

Underweight: 0 – 18.5
Healthy weight: 18.5 – 25
Overweight: 25 – 30
Obesity, class I: 30 – 35
Obesity, class II: 35 – 40
Obesity, class III: 40 and above

The core limitation

Three people. Same height, same weight, same BMI.

All three are 178 cm and 85 kg, which puts every one of them at a BMI of 26.8. BMI sees one number. Their bodies are not the same.

Strength athlete

Trains heavily, low body fat

12%

51%

37%

Body fat
Muscle
Bone, organs, water

BMI reads "overweight". Body fat is in the athletic range. The category is wrong about this person, and visibly so — which is the failure mode everyone knows about.

This is why the site pairs BMI with body fat percentage and lean body mass rather than treating the category as the answer.

The BMI formula

BMI = weight (kg) ÷ height (m)²

BMI = 703 × weight (lb) ÷ height (in)²

Both forms give the same number. The 703 factor simply converts pounds and inches into the metric equivalent — there is no separate “imperial BMI”.

What BMI does not tell you

It cannot separate muscle from fat. Muscle is denser than fat, so athletes and people who lift regularly are often classified as overweight while carrying low body fat.
It ignores fat distribution. Fat stored around the abdomen carries more metabolic risk than fat stored on the hips and thighs, and BMI cannot see the difference.
It was never designed for individuals. The formula was developed in the 1830s to describe populations, not to assess one person’s health.
Thresholds are not universal. Research shows health risk begins at different BMI values across ethnic groups, and the standard cutoffs fit older adults poorly.

Go deeper

Explore BMI in depth

Guides and tools covering how BMI works, where it breaks down, and which measures to use alongside it.

These sections are being published in stages. Each becomes a link when the guide goes live.

Common questions about BMI

What is BMI?: BMI, or body mass index, is your weight in kilograms divided by the square of your height in metres. It is a screening measure that sorts adults into weight categories, not a measure of health or body composition.
How do I calculate BMI?: Divide your weight in kilograms by your height in metres squared. In imperial units, multiply your weight in pounds by 703, then divide by your height in inches squared. Both give the same result.
What is a healthy BMI?: For adults, the World Health Organization defines 18.5 to 24.9 as the healthy range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classified as obesity.
Is BMI different for men and women?: No. Adult BMI uses the same formula and the same category thresholds for both. What differs is body composition: at an identical BMI, women typically carry a higher body fat percentage than men.
Why is BMI considered inaccurate?: BMI uses only height and weight, so it cannot tell muscle from fat or show where fat is stored. It commonly misclassifies muscular people as overweight, and it can miss excess body fat in people whose weight looks normal.