About this tool
Body Mass Index (BMI) is a simple screening measure that relates a person's weight to their height, calculated as weight in kilograms divided by height in meters squared (kg/m²) — or, in imperial units, 703 × weight in pounds divided by height in inches squared. The World Health Organization defines four standard adult categories from the result: underweight (below 18.5), normal weight (18.5 to 24.9), overweight (25 to 29.9), and obese (30 and above). This calculator computes BMI instantly in your browser, in either metric or imperial units, and also shows the weight range that would put you in the 'normal weight' category at your current height.
BMI is a useful population-level screening tool, but it is a crude one for any single individual: it cannot distinguish muscle from fat, so a heavily muscled athlete can show as 'overweight' despite very low body fat, while someone with little muscle mass can show as 'normal weight' despite a high body fat percentage. It also does not account for age, sex, bone structure, or ethnicity, and is not designed for pregnant people, children, or very short or very tall adults. Use this tool as one data point among many, not a diagnosis — for a full picture of your health, talk to a doctor or a registered dietitian.
Frequently asked questions
Is BMI an accurate measure of body fat?
No — BMI only relates height to weight and cannot distinguish muscle mass from fat mass, so athletes and very muscular people are often misclassified as "overweight" despite having low body fat. It's a useful, free, population-level screening tool, not a precise individual diagnosis — for a more direct estimate, try our body-fat-calculator, which uses actual body measurements instead.
Does BMI apply the same way to everyone?
Not entirely — the standard WHO thresholds shown here are widely used general-population guidelines, but many health organizations note that BMI interpretation can reasonably differ by factors like age, sex, and ethnicity (for example, some Asian population studies suggest health risks appear at somewhat lower BMI thresholds than the standard cutoffs). It also isn't designed for children/teens (who use age-and-sex-specific percentile charts instead), pregnant women, or the very elderly.