BMI calculator
Body mass index from height and weight, in metric or imperial, with what the number does and does not mean.
How it works
Body mass index is weight in kilograms divided by height in metres squared. It was devised in the 1830s by Adolphe Quetelet as a way of describing populations, not individuals, and that is still what it is best at.
The conventional bands are: under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, 30 and above obese. These thresholds are based largely on studies of European-ancestry populations, and several health bodies use lower cut-offs for people of South and East Asian descent, where cardiometabolic risk rises at a lower BMI.
BMI takes no account of body composition, and that is its central weakness: muscle is denser than fat, so athletes routinely score as overweight while someone with low muscle mass can sit in the healthy band with a high proportion of body fat. It also says nothing about where fat is carried, which matters more for risk than the total. Treat it as one crude screening number among several, not as a diagnosis.
This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.
Common questions
- How is BMI calculated?
- Weight in kilograms divided by height in metres squared. In imperial units it is weight in pounds divided by height in inches squared, multiplied by 703.
- What is a healthy BMI?
- The conventional healthy band is 18.5 to 24.9. Some health authorities use lower thresholds for people of South and East Asian descent, where risk rises at a lower BMI.
- Is BMI accurate?
- It is a rough population-level screening measure, not a measure of health. It cannot distinguish muscle from fat, so it misclassifies muscular people as overweight and can miss high body fat in people with low muscle mass.
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