BMI Calculator

Calculate your Body Mass Index in metric or imperial units.

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kg/cm or lb/ft+in
kilograms (kg)
centimetres (cm)
Enter your height and weight above
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What is BMI?

Body Mass Index (BMI) is a simple measure of body weight relative to height, calculated as weight in kilograms divided by height in metres squared: BMI = kg / m². It was developed in the 19th century by Belgian mathematician Adolphe Quetelet and is widely used by healthcare providers as an initial screening tool.

The WHO defines the following adult BMI categories: Under 18.5 (underweight), 18.5–24.9 (normal weight), 25–29.9 (overweight), 30–34.9 (obese class I), 35–39.9 (obese class II), and 40 and above (obese class III).

Limitations: BMI does not measure body fat directly and can misclassify muscular individuals as overweight. It also does not account for age, sex, ethnicity, or where fat is distributed on the body. Athletes often have a high BMI due to muscle mass rather than excess fat. Always consult a healthcare professional for a complete health assessment.

Frequently Asked Questions

BMI is a useful population-level screening tool, but it has significant limitations as an individual health measure. It cannot distinguish between fat and muscle mass, ignores fat distribution (abdominal fat carries higher health risk than fat in other areas), and uses thresholds calibrated primarily on European populations. Research suggests different BMI cut-offs may be more appropriate for Asian populations. Waist circumference, waist-to-hip ratio, and direct body composition measurements are more informative than BMI alone.

The standard adult BMI ranges (18.5–24.9 for normal weight) apply to adults aged 20 and over regardless of age or sex. For children and teenagers, BMI is interpreted differently — it's plotted on age- and sex-specific growth charts as a percentile rather than a fixed number, because children's body composition changes as they grow. This calculator uses the standard adult ranges. For children, consult a paediatrician.

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