BMI Calculator (Adults)
Body mass index (BMI) compares your weight with your height and is widely used as a quick screening measure for weight status in adults aged 20 and older. This calculator works in metric (cm, kg) and imperial (inches, pounds) units.
BMI is only a starting point. It does not tell the difference between muscle and fat, and its meaning can vary with age, pregnancy and ethnic background. A healthcare professional should interpret it alongside other measurements and your medical history.
BMI calculator (adults)
Body Mass Index with WHO adult categories and an Indian-population risk note.
Methodology & references
BMI = weight (kg) ÷ height (m)². In imperial units: BMI = 703 × weight (lb) ÷ height (in)². Categories follow the World Health Organization adult classification: underweight below 18.5, healthy 18.5–24.9, overweight 25–29.9, obesity 30 and above.
References
- WHO: Obesity and overweight fact sheet
- WHO Expert Consultation on BMI (Lancet, 2004) — Asian-population cut-offs
- CDC growth charts (for children and adolescents)
Limitations
- BMI does not distinguish muscle from fat and can misclassify athletes, elderly people and pregnant women.
- Adult categories must not be applied to children or adolescents under 19 years.
- For Asian Indian populations, risk may start at BMI ≥ 23; this calculator shows a note when that applies.
- The result is not a medical diagnosis. Consult a qualified healthcare professional before acting on it.
How to use this calculator
- Choose your units: metric (centimetres, kilograms) or imperial (inches, pounds).
- Enter your height and weight.
- Press Calculate and read your BMI together with its adult category.
- Read the methodology, limitations and references shown with the result before drawing conclusions.
Understanding your result
For adults, the World Health Organization classifies BMI as follows: below 18.5 is underweight, 18.5 to 24.9 is the healthy-weight range, 25 to 29.9 is overweight, and 30.0 and above is obesity (often further divided into classes I, II and III).
These are population screening bands, not personal targets, and some Asian populations use lower cut-offs — the calculator references are shown beside every result. Children and teenagers must never be classified with adult bands; they need age- and sex-specific BMI-for-age charts interpreted by a clinician.
Methodology & references
BMI = weight (kg) ÷ height (m)². In imperial units: BMI = 703 × weight (lb) ÷ height (in)². Categories follow the World Health Organization adult classification: underweight below 18.5, healthy 18.5–24.9, overweight 25–29.9, obesity 30 and above.
- WHO: Obesity and overweight fact sheet
- WHO Expert Consultation on BMI (Lancet, 2004) — Asian-population cut-offs
- CDC growth charts (for children and adolescents)
Limitations
- BMI does not distinguish muscle from fat and can misclassify athletes, elderly people and pregnant women.
- Adult categories must not be applied to children or adolescents under 19 years.
- For Asian Indian populations, risk may start at BMI ≥ 23; this calculator shows a note when that applies.
- The result is not a medical diagnosis. Consult a qualified healthcare professional before acting on it.
Frequently asked questions
Is BMI an accurate measure of my health?
BMI is a quick screening measure, not a diagnosis. It does not distinguish muscle from fat and may misclassify athletes, older adults, pregnant women and some ethnic groups. Use it as one starting point and discuss it with a healthcare professional.
Can I use this BMI calculator for children or teenagers?
No. This calculator applies adult categories only. Children and teenagers need age- and sex-specific BMI-for-age percentile charts interpreted by a paediatrician or trained clinician.
My BMI is outside the healthy range. What should I do?
A single number does not define your health. Discuss your BMI along with your waist measurement, medical history, diet, activity and any symptoms with a qualified healthcare professional before making changes.
Other health calculators