Body Mass Index (BMI) is the most widely used screening measure for weight status, adopted by the WHO and health services worldwide. This BMI calculator works in any units — centimeters, meters, feet & inches, kilograms, pounds or stone — and shows your BMI, category and where you sit on the healthy-weight scale as you type.
What is BMI?
BMI is a ratio of your weight to your height that gives a quick, standardized indication of whether your weight is in a healthy range for your height. It is not a diagnosis — it is a screening number that tells you whether a closer look is worthwhile. You can even type values directly (try "5'8" or "173 cm") and the marker slides along the scale as you go.
How BMI is calculated
The metric formula is BMI = weight (kg) ÷ height (m)². In imperial units it is BMI = 703 × weight (lb) ÷ height (in)². Worked example: at 5'8" (1.73 m) and 165 lb (75 kg), BMI = 75 ÷ 1.73² ≈ 25.1 — right at the boundary between the healthy and overweight ranges.
Adult BMI categories (WHO)
- Underweight: below 18.5
- Healthy weight: 18.5 – 24.9
- Overweight: 25 – 29.9
- Obese: 30 and above
What BMI can and cannot tell you
BMI is excellent for population screening but has well-known limits: it cannot distinguish muscle from fat, so muscular athletes often read "overweight" while carrying little fat; it is less reliable for adults over 65, for children (who use age-adjusted percentile charts), and during pregnancy. If your BMI is borderline, pair it with a waist measurement or a body fat estimate for a fuller picture, and consider your ideal weight range and daily calorie needs when planning changes.
For general information only — not medical advice. Talk to a healthcare professional before making significant changes.
Is BMI different for women?
The formula and the WHO adult cut-offs are identical for men and women — 25 is "overweight" for everyone. What differs is what the number hides: at the same BMI, women typically carry more body fat and men more muscle, so a woman and a man both at 24 are metabolically further apart than the shared number suggests. That's a reason to read borderline results with the body fat calculator or a waist measurement alongside, not a reason to use different BMI thresholds.
BMI vs body fat percentage
BMI is a ratio of weight to height; body fat percentage is an estimate of composition. They disagree exactly where it matters: a lean lifter can be "overweight" by BMI at 15% body fat, while a sedentary person can sit at a "healthy" 23 BMI with high visceral fat — the "normal-weight obesity" pattern. Rule of thumb: BMI to screen, composition to decide. If your BMI surprised you in either direction, the Navy-method body fat estimate takes two extra measurements and tells you which story is true.