BMI Calculator
Calculate your Body Mass Index (BMI) from height and weight in metric or imperial units, see your WHO category and healthy weight range.
How it works
BMI formula
BMI = weight (kg) / height (m)² Imperial: BMI = 703 × weight (lb) / height (in)²
BMI relates weight to height to estimate body fatness across large populations. The WHO categories are: under 18.5 underweight, 18.5–24.9 healthy weight, 25–29.9 overweight, and 30+ obesity.
Worked example
Someone 5 ft 9 in (69 inches) weighing 160 lb: BMI = 703 × 160 / 69² = 23.6, which falls in the healthy weight range (about 125–169 lb for that height).
Frequently asked questions
Is BMI accurate for everyone?
No. BMI cannot tell muscle from fat, so muscular people may read as overweight and people with low muscle mass may read as healthy despite excess fat. It also applies differently to children, pregnant women, and some ethnic groups.
What are the BMI categories?
WHO adult categories: below 18.5 is underweight, 18.5–24.9 is healthy weight, 25.0–29.9 is overweight, and 30.0 or above is obesity.
Is BMI different for children?
Yes. For ages 2–19, BMI is compared against age- and sex-specific growth percentiles rather than fixed cutoffs. This calculator uses adult categories.