BMI formula
BMI = weight (kg) ÷ height (m)². In US units: BMI = 703 × weight (lb) ÷ height (in)². Adult categories used by many health agencies: underweight under 18.5, healthy 18.5–24.9, overweight 25–29.9, obesity 30 and above.
BMI does not measure body fat, muscle, or health. Athletes can land in “overweight” with low fat. It is a screening number, not a diagnosis. Talk to a clinician about your own case.
Common questions
Is BMI different for children?
Yes. Children use age-and-sex percentiles, not these adult cutoffs. This page is for adults.
Why do some charts start obesity at 30?
That is the common WHO adult split. Some Asian-population guides use lower cutoffs.