BMI calculator

Your body mass index and the healthy weight range for your height, in metric or US units — plus what BMI does and doesn't measure.

Free, no sign-up

Before you use it

Works well for

  • A quick screening number for adults
  • Seeing the healthy weight range for your height
  • Metric and US units

Not the right tool for

  • Children, teens and pregnancy
  • Athletes and very muscular people
  • Diagnosing any health condition

How BMI is calculated

BMI = weight (kg) ÷ height (m)². For adults, the World Health Organization uses these ranges: under 18.5 underweight, 18.5–24.9 healthy weight, 25–29.9 overweight, 30 and above obesity (classes I, II and III from 30, 35 and 40).

What BMI doesn't tell you

  • It doesn't separate muscle from fat — muscular people can have a "high" BMI.
  • It says nothing about where fat is stored; waist size adds that information (see the waist-to-height ratio tool).
  • Some populations, including many Asian groups, face higher health risks at lower BMI, and some countries use lower cut-offs.
  • For children and teens, BMI must be compared with growth charts for age and sex.

Use BMI as a starting point for a conversation with a health professional, not as a diagnosis.

Frequently asked questions

Is BMI accurate?

It's a quick screening number that works reasonably at population level. For individuals, combine it with waist size and a professional assessment.

Does BMI work for children?

No — children and teens need age- and sex-specific growth charts.

Does it work during pregnancy?

No. Use pre-pregnancy weight for planning and follow your prenatal care team's guidance.