How do I calculate BMI from height and weight?

Divide your weight in kilograms by the square of your height in metres. For example, 68 kg at 1.72 m: 68 / (1.72)² ≈ 23.0. The calculator does this instantly and shows your category and healthy weight range.

What BMI is considered normal?

By WHO classification, a normal BMI is 18.5 to 24.9. Below 18.5 is underweight, 25.0–29.9 is overweight and 30 or more is obesity. The lowest health risk in studies sits around BMI 22–25.

Is BMI accurate for athletes?

No. Muscle is heavier than fat, so athletic people get a high BMI that can wrongly read as “overweight”. In that case add your measurements — the calculator estimates body fat and recalculates a healthy weight from body composition.

How does body-composition healthy weight differ from the BMI norm?

The BMI norm is based on height alone and is the same for everyone. Body-composition healthy weight is derived from your lean (muscle) mass and a target body-fat range, so it’s personal: for a muscular person it’s higher than the lower edge of the BMI norm.

Does BMI differ for men and women?

The formula and WHO category thresholds are the same for adult men and women. But body composition differs — women naturally carry more body fat — so when refining by measurements the calculator uses different target ranges for men and women.

Body mass index (BMI) calculator

Body mass index (BMI) is a quick indicator of whether your weight is healthy for your height. Enter your height and weight — the calculator shows your BMI, the WHO category and a healthy weight range. Add a few tape measurements and the model refines the estimate using body composition, so people with more muscle aren’t overrated.

Calculate your BMI and healthy weight

Enter your height and weight — the result appears instantly.

BMI norms: category table (WHO)

Adult body-weight classification by body mass index (World Health Organization).

BMI, kg / m²	Category
below 16.0	Severe underweight
16.0–16.9	Moderate underweight
17.0–18.4	Mild underweight
18.5–24.9	Normal
25.0–29.9	Overweight
30.0–34.9	Obesity class I
35.0–39.9	Obesity class II
40.0 and above	Obesity class III

How BMI is calculated: the formula

Body mass index is your weight in kilograms divided by the square of your height in metres (BMI = weight / height²). For example, at 1.72 m and 68 kg: 68 / (1.72 × 1.72) ≈ 23.0 kg / m².

For adults the value doesn’t depend on sex or age, which is why it works as a universal quick indicator — and also why it’s only approximate: it doesn’t account for what your weight is made of.

Healthy weight for your height

The normal BMI range of 18.5–24.9 maps to a weight corridor for each height, which the calculator works out automatically. The lower bound (BMI 18.5) is the lean edge of normal; the lowest mortality in large cohorts sits around BMI 22–25, so the upper half of the range is a more realistic target.

Add your neck, waist and (for women) hip measurements and the calculator estimates body fat with the US Navy method, derives lean mass and recalculates a healthy weight for your build. For a muscular person that personal weight comes out above the lean edge — as it should.

Limitations of BMI

BMI doesn’t distinguish muscle from fat and ignores where fat sits. It runs high for athletes with lots of muscle and low for older people who’ve lost muscle. Oedema, pregnancy and body-frame differences also distort it.

So BMI is a starting point, not a diagnosis. A fuller picture comes from body composition (body fat), waist circumference and metabolic lab values — glucose, lipids and thyroid hormones.

BMI in children and teenagers

The adult BMI corridor doesn’t apply to children and teenagers: weight and height are assessed as percentiles and z-scores for age and sex, using dedicated WHO growth charts rather than a single 18.5–24.9 norm.

Frequently asked questions

Divide your weight in kilograms by the square of your height in metres. For example, 68 kg at 1.72 m: 68 / (1.72)² ≈ 23.0. The calculator does this instantly and shows your category and healthy weight range.
By WHO classification, a normal BMI is 18.5 to 24.9. Below 18.5 is underweight, 25.0–29.9 is overweight and 30 or more is obesity. The lowest health risk in studies sits around BMI 22–25.
No. Muscle is heavier than fat, so athletic people get a high BMI that can wrongly read as “overweight”. In that case add your measurements — the calculator estimates body fat and recalculates a healthy weight from body composition.
The BMI norm is based on height alone and is the same for everyone. Body-composition healthy weight is derived from your lean (muscle) mass and a target body-fat range, so it’s personal: for a muscular person it’s higher than the lower edge of the BMI norm.
The formula and WHO category thresholds are the same for adult men and women. But body composition differs — women naturally carry more body fat — so when refining by measurements the calculator uses different target ranges for men and women.

Thyroid, glucose and hormones all affect your weight

BMI is just one indicator. Upload your lab results — AI explains what’s behind your weight and connects the values together.

Decode my lab results

This calculator is for reference and information only and is not a diagnosis or prescription. A doctor assesses weight and health risks with the full picture in mind.