Units, Weight, Height, Extra inches (US only)
BMI Calculator
Work out your body mass index from height and weight, in metric or US units.
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How this calculator works
BMI divides your weight by the square of your height. It is a quick screening number for adults: it does not measure body fat directly, so athletes with a lot of muscle and older adults with little muscle can land in a misleading category. Use it as a starting point, not a diagnosis.
Formula
- BMI = weight (kg) / height (m)²
- US units: BMI = 703 × weight (lb) / height (in)²
- Healthy weight range = 18.5 × height (m)² to 24.9 × height (m)²
Worked example
70 kg at 175 cm
- Units
- Metric (kg, cm)
- Weight
- 70
- Height
- 175
ResultBMI 22.9
Normal weight on the WHO adult scale.
WHO adult BMI categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 - 24.9 | Normal weight |
| 25.0 - 29.9 | Overweight |
| 30.0 - 34.9 | Obesity class I |
| 35.0 - 39.9 | Obesity class II |
| 40.0 and above | Obesity class III |
Things to keep in mind
- The categories apply to adults aged 20 and over. Children and teens are assessed with age- and sex-specific percentile charts.
- Some health bodies use lower cut-offs for people of Asian descent (overweight from 23).
- For general information only. It is not medical advice; talk to a health professional about your own situation.
Frequently asked questions
What is a healthy BMI?
For most adults the World Health Organization treats 18.5 to 24.9 as the normal range. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or more is obesity.
Is BMI accurate for muscular people?
Not very. BMI cannot tell muscle from fat, so a muscular person can score as overweight with low body fat. Waist size or a body fat estimate gives a better picture in that case.
Does BMI work the same for men and women?
The formula and the adult categories are the same. Women typically carry more body fat than men at the same BMI, which is one reason BMI is only a screening tool.
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Results are estimates based on the values you enter and the published method shown above. They do not replace professional medical, financial or legal advice. Method reviewed October 7, 2026. About this site