How is BMI calculated?

BMI is your weight in kilograms divided by the square of your height in metres. Imperial entries are converted to kilograms and metres first.

What is a healthy BMI?

For adults, a BMI between 18.5 and 24.9 is considered the normal, healthy range under the WHO classification.

Does BMI work for athletes?

Not well. Muscle weighs more than fat, so very muscular people can land in the overweight band despite low body fat. Pair BMI with a body-fat estimate.

Is BMI suitable for children?

No. Children and teenagers use age- and sex-specific BMI percentiles instead of the fixed adult cut-offs used here.

Can I switch between metric and imperial?

Yes. Pick the unit system at the top and enter height and weight in those units; the result is the same BMI either way.

Can I share my result?

Yes. Use Share to copy a link that reopens the calculator with the same height, weight and units.

BMI calculator

Enter your height and weight, choose metric or imperial, and see your BMI, weight category and healthy-weight range as you type.

BMI is your weight in kilograms divided by your height in metres squared. A BMI of 18.5–24.9 is the normal range for adults.

Units

Height

Weight

Your BMI

22.9

Normal weight

Healthy weight range: 56.7–76.5 kg

The gauge shows where your BMI sits across the four WHO bands, and the healthy range tells you the weight that would put you in the normal band for your height.

How does it work?

Imperial entries are converted to kilograms and metres first. WHO bands: under 18.5, 18.5–24.9, 25–29.9, 30 and over.

BMI formula

\text{BMI} = \dfrac{\text{weight (kg)}}{\text{height (m)}^2}

weight: Body weight in kilograms.
height: Standing height in metres.

A person of 70 kg and 1.75 m has a BMI of 70 ÷ 1.75² ≈ 22.9 (normal).

Expert tips

Very muscular people can score as overweight although their body fat is low.
BMI is a screening tool, not a diagnosis — discuss your result with a health professional.

Method & sources

We divide your weight in kilograms by your height in metres squared. The result is compared to WHO adult cut-offs for underweight, normal weight, overweight, and obesity. You enter your own height and weight — the calculator does not measure body fat or access medical records.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

Body mass index (BMI) — WHO classification — World Health Organization, verified 2026-06-10

How we calculate

Uses the WHO adult cut-offs: underweight under 18.5, normal 18.5–24.9, overweight 25–29.9, obese 30 and over.
BMI screens for weight relative to height; it does not measure body fat or distinguish muscle from fat.
The bands are for adults aged 20 and over and are not adjusted for children, athletes, pregnancy or specific ethnic groups.

Limitations

Very muscular people can score as overweight although their body fat is low.
BMI is a screening tool, not a diagnosis — discuss your result with a health professional.

Rounding

BMI is shown to one decimal place. Imperial entries are converted to kilograms (1 lb = 0.45359237 kg) and metres (1 in = 0.0254 m) before the standard metric formula is applied.

What BMI tells you

Body Mass Index (BMI) compares your weight to your height to screen for underweight, healthy weight, overweight and obesity. It is a quick first check, not a measure of body fat or overall health.

How to use it

Choose metric (cm, kg) or imperial (in, lb).
Enter your height.
Enter your weight.
Read your BMI, category and healthy-weight range below.

The WHO weight categories

Underweight: BMI below 18.5
Normal weight: BMI 18.5 to 24.9
Overweight: BMI 25 to 29.9
Obese: BMI 30 and over

A worked example

Someone 1.75 m tall weighing 70 kg has a BMI of 70 ÷ 1.75² ≈ 22.9, which is in the normal range. Their healthy-weight range for that height is roughly 57–76 kg.

Why BMI has limits

BMI does not separate muscle from fat or show where fat sits, so very muscular people may score high while carrying little fat. Use it alongside other measures and professional advice, not on its own.

FAQ

How is BMI calculated?: BMI is your weight in kilograms divided by the square of your height in metres. Imperial entries are converted to kilograms and metres first.
What is a healthy BMI?: For adults, a BMI between 18.5 and 24.9 is considered the normal, healthy range under the WHO classification.
Does BMI work for athletes?: Not well. Muscle weighs more than fat, so very muscular people can land in the overweight band despite low body fat. Pair BMI with a body-fat estimate.
Is BMI suitable for children?: No. Children and teenagers use age- and sex-specific BMI percentiles instead of the fixed adult cut-offs used here.
Can I switch between metric and imperial?: Yes. Pick the unit system at the top and enter height and weight in those units; the result is the same BMI either way.
Can I share my result?: Yes. Use Share to copy a link that reopens the calculator with the same height, weight and units.

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