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BMI Calculator
Free BMI calculator for adults: body mass index in metric or US units, WHO weight category and your healthy weight range for your height.
Runs in your browser. For adults aged 20 and over.
How to use the BMI Calculator
- Choose metric or imperial units.
- Enter your height and weight.
- Read your BMI, category and healthy weight range.
What is BMI?
Body Mass Index is your weight in kilograms divided by your height in metres squared. It is a quick screening number, used by the World Health Organization to group adults by weight status.
BMI = weight (kg) ÷ height (m)²
| BMI | Category (adults) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
Worked example
70 kg at 175 cm: 70 ÷ 1.75² = 22.9, which is in the normal range.
Limits of BMI
BMI does not separate muscle from fat, and it does not account for age, sex or body shape. Athletes can score high with low body fat. Some Asian populations face health risks at lower BMI values than the standard cut-offs. For children and teenagers use age-based growth charts.
Frequently asked questions
How do I calculate BMI?
Divide weight in kilograms by height in metres squared. In pounds and inches, multiply weight by 703 and divide by height squared.
What is a healthy BMI?
For adults, 18.5 to 24.9 is considered the normal range by the WHO.
Is BMI accurate for athletes?
Not always, because muscle is heavy. Waist size and body-fat percentage add useful context.
Can I use this for children?
No. Children's BMI is compared with age and sex percentiles, which this tool does not use.