BMI Calculator
Calculate Body Mass Index in metric or imperial units with WHO classification.
WHO BMI classification
What is BMI and how is it calculated?
Body Mass Index (BMI) is a simple numerical measure calculated by dividing body weight (in kilograms) by height squared (in metres): BMI = kg / m². It was developed in the 19th century by Belgian mathematician Adolphe Quetelet as a population-level screening tool, not as a diagnostic for individual health. The World Health Organization uses BMI thresholds to classify weight status at a population level.
Frequently asked questions
What are the limitations of BMI?
BMI does not distinguish between muscle and fat mass. A muscular athlete may have a BMI in the "overweight" range despite having very low body fat. Conversely, someone can have a "normal" BMI with high body fat and low muscle mass. Age, sex, ethnicity, and bone density also affect body composition in ways BMI cannot capture. It is a starting point, not a diagnosis.
What is the formula for imperial BMI?
BMI (imperial) = (weight in pounds / height in inches²) × 703. The 703 factor converts the result from pounds/inch² to the standard kg/m² scale so the same WHO thresholds apply.
What is a healthy BMI range?
The WHO defines 18.5–24.9 as the normal weight range for adults. Below 18.5 is underweight; 25–29.9 is overweight; 30 and above is obese. These thresholds are the same for both men and women in the WHO classification, though some health bodies use age-adjusted or ethnicity-adjusted ranges.
