BMI is a screening tool, not a diagnosis. It ignores muscle mass, bone density and fat distribution, so very muscular people can score high while some older adults with low muscle can score normal. Use it as a starting point alongside waist measurements and, ideally, advice from a health professional. To look at body composition in more detail, try the Body Fat Calculator.
Calculator
Formula used
BMI = weight (kg) ÷ height (m)² · imperial: BMI = 703 × weight (lb) ÷ height (in)²
How to use the BMI Calculator
- Choose metric or imperial units.
- Enter your height and weight.
- Read your BMI and the category it falls in.
- Check the healthy weight range for your height.
About this tool
The BMI Calculator is built for speed and accuracy: every calculation runs in your browser, so your data never leaves your device and the result updates as you type. It works equally well on a phone, a tablet or a desktop, and it is free to use as many times as you like.
Common use cases
- Checking whether your weight is in a healthy range.
- Tracking progress during a fitness programme.
- Preparing information for a health check.
- Setting a realistic target weight.
Tips for the best result
- Use the latest figures you have - even a small change in rate or term can shift the outcome by hundreds.
- For annual figures, divide by 12 to get a monthly number you can compare with the result.
- Bookmark this page and revisit the calculation as the inputs change.
Frequently asked questions
Is BMI accurate for athletes?
Not really. Muscle weighs more than fat, so very muscular people can be classed as overweight despite low body fat. Body fat percentage or waist measurement is more informative for them.
Does BMI differ by age or sex?
The same formula and thresholds are used for adult men and women. Separate growth charts are used for children and teenagers.
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