BMI calculator — body mass index with healthy weight range
Work out your body mass index in metric or imperial units, see which WHO band it falls in, and — more usefully — the healthy weight range for your height.
Runs entirely in your browser — nothing is uploaded.
BMI is a population screening measure, not a diagnosis. It cannot tell muscle from fat, so it misclassifies athletes as overweight and can miss excess fat in older or less muscular people. It also does not account for where fat is carried, which matters more for health risk than the total.
How to use
- Pick your units. Metric (kg and cm) or imperial (pounds and feet/inches).
- Enter weight and height. The result updates as you type.
- Read the range, not just the number. The healthy weight range for your height is more actionable than a single BMI figure.
Questions
How is BMI calculated?
Weight in kilograms divided by height in metres squared. For 70 kg at 1.75 m: 70 ÷ (1.75 × 1.75) = 22.9. Imperial inputs are converted to metric first.
What are the categories?
The WHO adult bands are: under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30–34.9 obese class I, 35–39.9 class II, 40 and above class III.
Why is BMI criticised?
Because it cannot distinguish muscle from fat, and ignores where fat is carried. A rugby player and someone carrying excess visceral fat can share a BMI of 28 with completely different health risks. Waist circumference and waist-to-height ratio predict cardiometabolic risk better.
Does BMI work for children or athletes?
Not as given here. Children and teenagers need age- and sex-specific percentile charts, not adult thresholds. Muscular athletes are routinely misclassified as overweight. It is also less reliable for older adults, who lose muscle while gaining fat at a stable weight.