BMI Calculator

Body Mass Index (BMI) is a measure of body fat based on height and weight. The formula is BMI = weight (kg) ÷ height² (m²). For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75²) = 22.9. In imperial units, multiply the result by 703.

The World Health Organization defines BMI categories as: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obese (30 and above). These thresholds were established from population studies linking BMI to health outcomes such as cardiovascular disease and diabetes.

BMI is a useful population-level screening tool but has limitations for individuals. It does not distinguish between muscle and fat mass — athletes may have a high BMI despite low body fat. Age, sex, ethnicity, and fitness level all affect what a healthy BMI means for a particular person. Always consult a healthcare professional for personalized assessment.

For most adults, a BMI between 18.5 and 24.9 is considered healthy according to WHO guidelines. Some research suggests that Asian populations may have elevated health risks at lower BMI thresholds, with some health organizations recommending overweight classification starting at 23 for these groups.

This calculator is designed for adults aged 18 and over. For children and teenagers, BMI is interpreted differently using age- and sex-specific percentile charts, because body fat percentage changes significantly during growth. A pediatrician should assess BMI for anyone under 18.