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BMI calculator

Body mass index compares weight with height. It is a quick screening number for adults, not a diagnosis, and it does not account for muscle mass, age or body shape.

Your BMI–
Category–

Key: / jumps to the first field

Results are for information only.

How to use it

  1. Choose metric or imperial units at the top of the page.
  2. Enter your height and weight.
  3. Read your BMI and the matching adult category.

How it works

BMI divides weight by the square of height. The categories are the adult cut-offs used by the World Health Organization and the US CDC: under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, 30 and above obesity.

BMI = kg ÷ m² · BMI = 703 × lb ÷ in²

Worked example

1.75 m and 70 kg: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9, in the healthy range. In US units, 5 ft 9 in (69 in) and 150 lb: 703 × 150 ÷ 4,761 = 22.2.

Assumptions and limits

  • BMI is a screening number, not a diagnosis. It can't tell muscle from fat, so athletes often read “overweight” while some older adults read “healthy” despite low muscle mass.
  • It says nothing about where fat sits. Waist size is a useful second check.
  • Some health bodies use lower cut-offs for people of Asian descent, and BMI tends to overestimate fatness in some Black adults.
  • Children and teens need age- and sex-specific percentile charts, not these adult bands. Pregnancy is also excluded.

Sources

World Health Organization, “Obesity and overweight” fact sheet and the WHO BMI classification for adults. US Centers for Disease Control and Prevention (CDC), “Adult BMI Categories” and “About Child and Teen BMI”.

Frequently asked questions

What is the BMI formula?

BMI equals weight in kilograms divided by height in meters squared. In imperial units it is 703 × pounds ÷ inches².

What is a healthy BMI range?

For most adults the WHO considers 18.5 to 24.9 a normal range. Some health bodies use lower cut-offs for certain populations.

Is BMI valid for children or athletes?

Not directly. Children need age-specific percentile charts, and muscular people can show a high BMI without excess fat. Ask a health professional.