Is BMI accurate for athletes?

No; muscle is denser than fat, so muscular people routinely land in overweight bands while carrying little excess fat. Use body-fat or waist measures alongside.

Do children use this calculator?

No. Children and teens need age- and sex-specific percentile charts from a paediatric provider.

For most adults the WHO defines 18.5–24.9 as the normal range, though optimal risk profiles vary by ethnicity and individual factors.

How do I use imperial units?

Switch the Units selector to Imperial and type your weight in pounds and height in inches; conversion happens automatically.

Health

BMI Calculator

What this does

Calculate your Body Mass Index from weight and height in metric or imperial units, with WHO categories and the healthy weight range for your height.

Enter your details

Runs in your browser

How to use it

Using the bmi calculator

01
Pick your units
Choose metric to enter kilograms and centimetres, or imperial to enter pounds and inches.
02
Enter weight and height
Use your current measurements; morning weigh-ins before eating are most consistent.
03
Read your category and range
The result shows your BMI, WHO band, and the healthy weight window for your height.

Good to know

What BMI measures; and what it does not

BMI is a screening ratio, not a body composition test. It correlates with body-fat percentage at population scale but is blind to muscle mass, bone density and fat distribution. A rugby prop and a sedentary office worker of identical height and weight share a BMI despite very different health profiles.

Why the healthy range is a range

Mortality curves across large cohorts are U-shaped but flat between roughly BMI 18.5 and 24.9, which is why the band spans nearly 15 kg at average height rather than naming a single ideal number.

Pair it with other measures

Waist-to-height ratio captures central fat that BMI misses.
Body-fat calipers or Navy circumference estimates add composition detail.
Trends over time matter more than any single reading.

How it's calculated

The math behind this calculator

BMI = weight(kg) / height(m)²
Imperial input converted: lb × 0.45359237 → kg; in × 2.54 → cm

Body Mass Index divides your weight in kilograms by the square of your height in metres. The resulting number places you into one of four World Health Organization categories, from underweight to obese.

We also convert your BMI back into an absolute healthy weight range; between BMI 18.5 and 24.9 at your exact height; so you can see what a change on the scale means.

Assumptions & limitations

Applies to adults aged 20 and over.
Does not distinguish muscle from fat; athletes often score "overweight" despite low body fat.
Ethnicity-specific thresholds (e.g. lower cutoffs for some Asian populations) are not applied.

Worked example

A person weighing 70 kg at 175 cm has a BMI of about 22.86; comfortably inside the normal-weight band, whose healthy range at this height runs roughly 57–76 kg.

FAQ

Frequently asked questions

Is BMI accurate for athletes?: No; muscle is denser than fat, so muscular people routinely land in overweight bands while carrying little excess fat. Use body-fat or waist measures alongside.
Do children use this calculator?: No. Children and teens need age- and sex-specific percentile charts from a paediatric provider.
What BMI is healthy?: For most adults the WHO defines 18.5–24.9 as the normal range, though optimal risk profiles vary by ethnicity and individual factors.
How do I use imperial units?: Switch the Units selector to Imperial and type your weight in pounds and height in inches; conversion happens automatically.

Keep exploring