Body mass index (BMI) is the quick screening number doctors, insurers and fitness apps use to compare weight with height. This free BMI calculator works in both metric (centimetres and kilograms) and imperial units (feet, inches and pounds), so it suits readers in the US, UK, Canada, Australia and Germany alike. Enter your height and weight and you'll instantly see your BMI to one decimal place, the World Health Organization category it falls into, and the weight range that would put someone of your height in the "healthy" band. We also show the exact formula, so you can check the maths yourself. A word of honesty: BMI is a rough screening tool, not a diagnosis. It doesn't know how much of your weight is muscle, how old you are, or where you carry fat, which is why athletes often score as "overweight" and why some health services use different cut-offs for people of South Asian, Chinese or Black African heritage. Use the number as a conversation starter with a doctor, not a verdict. Everything runs in your browser and nothing you type is stored or sent anywhere.
Calculate your BMI
For adults 18+. Not medical advice. Children and teens need age- and sex-specific BMI percentiles.
How to use the BMI calculator
- Choose metric or imperial units.
- Enter your height and current weight.
- Read your BMI, category and healthy weight range. Results update as you type.
The BMI formula and WHO categories
BMI = weight (kg) ÷ height (m)². In imperial units it's 703 × weight (lb) ÷ height (in)².
| BMI | WHO category (adults) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Obesity class I |
| 35 – 39.9 | Obesity class II |
| 40 or more | Obesity class III |
FAQ
Is BMI accurate?
It’s a useful population-level screen but a blunt individual measure. It can overestimate fat in muscular people and underestimate it in older adults. Waist size and a doctor’s assessment add important context.
Is BMI different for men and women?
The adult formula and WHO cut-offs are the same for both. For children and teens, results are compared with age- and sex-specific growth charts instead.
Do Asian people use different BMI cut-offs?
Some health bodies, such as the UK’s NICE, recommend lower thresholds (for example 23 and 27.5) for people of South Asian, Chinese and some other ethnic backgrounds because of higher health risk at lower BMIs.
Is my data saved?
No. The calculation runs in your browser. Nothing is stored or sent.
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