Body Mass Index calculator with health category output.
The BMI (Body Mass Index) Calculator computes BMI from height and weight using the formula BMI = weight(kg) ÷ height(m)². BMI is a population-level screening tool used to categorize weight status: underweight (<18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (≥30). It is a simple initial indicator, not a diagnostic tool — BMI does not measure body fat percentage, muscle mass, or fat distribution. Athletes and people with high muscle mass often have elevated BMI despite being healthy.
Underweight: below 18.5. Normal weight: 18.5–24.9. Overweight: 25–29.9. Obese class I: 30–34.9. Obese class II: 35–39.9. Obese class III (severe): 40 and above. Different thresholds apply for Asian populations (overweight begins at 23).
No. BMI cannot distinguish muscle from fat. A muscular athlete with low body fat may have a BMI of 28 (overweight category) because muscle is denser than fat. For athletes, body fat percentage (via DEXA scan or skinfold measurement) is more accurate.
Children use a different calculation: BMI-for-age percentile, which compares BMI to other children of the same age and sex. An adult BMI calculator should not be used for children under 18.