Calculate your Body Mass Index with imperial or metric units
| Underweight | < 18.5 |
| Normal weight | 18.5 - 24.9 |
| Overweight | 25.0 - 29.9 |
| Obese | ≥ 30.0 |
BMI: Useful Starting Point, Limited Endpoint Calculate your Body Mass Index from your height and weight. BMI is one of the most widely used health screening tools in the world — and one of the most widely misunderstood. BMI was invented by Belgian mathematician Adolphe Quetelet in the 1830s. Quetelet was not a physician and explicitly stated that his formula was designed for population-level statistics, not individual health assessment. He wanted a single number to describe the "average man" in population datasets. The formula — weight in kilograms divided by height in meters squared — was adopted for clinical use in the 1970s when the medical community needed a quick, equipment-free screening tool. It has been a standard fixture in healthcare ever since. The formula's core limitation is that it cannot distinguish between fat mass and lean mass. Muscle is significantly denser than fat. A professional athlete with 10% body fat and substantial muscle mass can have the same BMI as a sedentary individual with 30% body fat — both might score 27, classified as "overweight" by WHO standards. The formula sees mass relative to height but has no mechanism to know where that mass comes from. Additional systematic limitations: BMI was calibrated on European male populations. It tends to underestimate adiposity in shorter individuals and overestimate it in taller ones due to the mathematical properties of the formula. It also misclassifies across ethnic groups — many Asian health organizations use a lower overweight threshold of 23 rather than 25 because Asian populations face elevated metabolic risk at BMIs that Western guidelines treat as normal. Clinicians who see a BMI result use it as a single data point alongside waist circumference, waist-to-hip ratio, blood pressure, blood glucose, lipid panels, and clinical judgment. Waist circumference above 40 inches in men and 35 inches in women is associated with elevated metabolic risk regardless of BMI. Body fat percentage measured via DEXA scan or bioelectrical impedance provides substantially more information. Waist-to-height ratio — simply your waist circumference divided by your height — correlates better with cardiovascular risk than BMI in many studies. BMI is a useful first screen and a convenient number for tracking trends in your own health over time. What it is not is a diagnosis or a complete picture.
Belgian mathematician Adolphe Quetelet invented it in the 1830s as a population statistics tool — not a clinical one. He explicitly said it was not meant for individual health assessment. It was adopted for clinical screening in the 1970s.
No. BMI cannot distinguish muscle from fat. Athletes with low body fat and high muscle mass are routinely classified as overweight or obese. For athletic individuals, body fat percentage or waist-to-height ratio are more informative.
Clinicians consider waist circumference, waist-to-hip ratio, blood pressure, blood glucose, lipid panels, and overall clinical presentation. Waist circumference above 40 inches in men or 35 inches in women signals elevated metabolic risk regardless of BMI.