BMI Calculator
Enter your height and weight to get your Body Mass Index, the WHO weight category it falls into, and the healthy weight range for your height. Works in both metric and imperial units.
How this calculation works
BMI divides your weight in kilograms by the square of your height in metres: BMI = kg ÷ m². Imperial inputs are converted to metric first.
The World Health Organization bands are: under 18.5 = underweight, 18.5–24.9 = normal, 25–29.9 = overweight, 30+ = obese.
The healthy weight range is the weight that would place your BMI between 18.5 and 24.9 at your current height.
Worked example
How to read your BMI
The World Health Organization groups adult BMI into these ranges:
| BMI | Category | Note |
|---|---|---|
| Below 18.5 | Underweight | May signal under-nutrition |
| 18.5 – 24.9 | Normal weight | Lowest health risk for most adults |
| 25.0 – 29.9 | Overweight | Raised risk |
| 30.0 – 34.9 | Obese (class I) | Moderate risk |
| 35.0 – 39.9 | Obese (class II) | High risk |
| 40.0 and above | Obese (class III) | Very high risk |
Cut-offs differ by population
The standard ranges were derived largely from European populations. For many Asian groups, health risks rise at lower BMI values, so the WHO suggests additional Asian cut-offs: overweight from about 23 and obese from about 25. If you are of Asian descent, treat the standard "normal" ceiling with extra caution.
What BMI cannot tell you
BMI is only weight and height. It cannot distinguish muscle from fat, so very muscular people (athletes, weightlifters) often read as "overweight" while being lean. It also ignores where fat sits — visceral fat around the organs is more harmful than fat on the hips.
BMI is not valid for children and teenagers, who should use age-and-sex percentile charts, nor is it reliable for pregnant women or the very elderly, who may carry less muscle.
Use waist and body-fat alongside BMI
Two quick companions add a lot of insight. Waist-to-height ratio should ideally stay below 0.5 (your waist less than half your height). Body-fat percentage, from calipers or a smart scale, captures composition that BMI misses. Read BMI as a first screen, not a diagnosis.