Calculate your Body Mass Index (BMI) and check if your weight is healthy.
BMI (Body Mass Index) is a number calculated from your height and weight. It's widely used as a screening tool because it's simple and requires no equipment. But it's also widely misunderstood. This calculator gives you your BMI and explains what it does — and doesn't — tell you about your health.
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = (weight (lbs) × 703) ÷ height (inches)²
Example: A person who is 175cm (1.75m) and weighs 70kg has a BMI of 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9. This falls in the "Normal weight" category.
BMI is a ratio of weight to height. It has no way to distinguish between muscle and fat. A professional athlete with very low body fat can have a BMI of 27 (classified as "overweight") because muscle is denser than fat. Conversely, someone with a "normal" BMI of 23 can have high body fat percentage if they have low muscle mass — a condition sometimes called "skinny fat" or normal-weight obesity.
BMI also doesn't account for age, sex, or ethnicity. Older adults naturally lose muscle mass, so the same BMI represents more body fat than in younger adults. Research suggests that Asian populations have higher health risks at lower BMI thresholds — some health organizations use adjusted cutoffs for Asian patients.
Despite its limitations, BMI is a reasonable population-level screening tool. For most non-athletic adults, BMI correlates reasonably well with body fat percentage and health risk. It's useful for tracking changes over time in the same person, for initial screening before more detailed assessment, and for large-scale public health research where individual measurements aren't practical.
All calculations happen in your browser. No health data is stored or transmitted anywhere.
BMI under 18.5 is underweight, 18.5-24.9 is normal weight, 25-29.9 is overweight, and 30+ is obese. These are general population guidelines from the WHO. They do not account for muscle mass, bone density, age, or ethnicity.
BMI is a simple screening tool, not a diagnostic measure. It can misclassify muscular athletes as overweight and miss unhealthy body fat distribution in people with normal BMI. Waist circumference, body fat percentage, and other metrics give a more complete picture.
BMI = weight (kg) divided by height (m) squared. For example, 70kg at 1.75m: 70 divided by (1.75 x 1.75) = 22.9. In imperial: BMI = (weight in lbs x 703) divided by height in inches squared.
Standard adult BMI categories do not apply to children. For ages 2-19, BMI is plotted on age- and sex-specific growth charts to determine percentile. A pediatrician should interpret BMI for children.
The standard healthy BMI range (18.5-24.9) applies to adults 20 and older. For older adults (65+), some research suggests a slightly higher BMI (22-27) may be associated with better outcomes. Always consult a healthcare provider for personalized guidance.