BMI Calculator (Adult & Child)
Calculate Body Mass Index with metric or US units. Adults get BMI, category and healthy weight range.
For children (2–19), BMI is shown with a note that classification requires age‑ and sex‑specific growth charts.
How BMI is calculated
BMI = weight ÷ height². In metric this is kilograms divided by meters squared. In US units, BMI equals 703 × pounds ÷ inches². Adults are categorized using standard cut‑offs; for children, BMI must be compared against age‑ and sex‑specific growth charts.
BMI
—
Category (adult)
—
Healthy weight (adult)
— (BMI 18.5–24.9)
Underweight • Healthy • Overweight • Obesity
Frequently Asked Questions
- What are adult BMI categories?
- Underweight < 18.5; Healthy 18.5–24.9; Overweight 25–29.9; Obesity ≥ 30 (Class I 30–34.9, Class II 35–39.9, Class III ≥ 40).
- Why is child BMI different?
- Children’s BMI changes with age and differs by sex. Classification uses percentiles (Underweight <5th, Healthy 5th–<85th, Overweight 85th–<95th, Obesity ≥95th). This page reports BMI; percentile charts can be embedded if you’d like.
- Do you store any data?
- No. Everything runs locally in your browser.
- Is this tool a medical advice?
- No. This tool is for educational purposes only and it is not a medical advice.