BMI Calculator
Calculate Body Mass Index in metric or imperial — with WHO category context.
Free · No sign-up · Runs locally in your browser · Also available in Chinese (中文)
What is BMI Calculator?
Body Mass Index divides weight by the square of height (kg/m²) and sorts the result into WHO categories: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30+ obese. It was designed as a population-level screening statistic — cheap, fast and consistent across large groups.
This calculator works in metric and imperial, computes the exact value and places it on the scale with the category boundaries visible. Treat the number as one signal among many: BMI does not distinguish muscle from fat, and that limitation matters for athletes, older adults and children.
How to use it
- 1Choose metric (kg/cm) or imperial (lb/ft+in) units.
- 2Enter your height and weight.
- 3Read your BMI value and its WHO category.
- 4Use the boundary markers to see how far you are from the next category.
Common use cases
- A quick self-check before or during a fitness program.
- Filling in health forms and insurance questionnaires that ask for BMI.
- Understanding where the category boundaries fall for your own height.
Frequently asked questions
▸Is BMI accurate for muscular people?
No — muscle is denser than fat, so athletes often score 'overweight' while carrying little body fat. Pair BMI with waist measurement or body-fat percentage for a real picture.
▸Does BMI work for children?
Not with adult cutoffs. Children and teens are assessed with age- and sex-specific percentile charts — use a pediatric BMI tool for anyone under 18.