How to use the BMI Calculator
- Choose metric (cm, kg) or US/imperial (ft, in, lb).
- Enter your height and weight.
- Read your BMI, your category and the healthy weight range for your height.
What does this tool do?
Body mass index divides your weight by the square of your height. It's a quick screening number that doctors and public health agencies use to flag possible weight-related health risks in adults.
BMI can't tell muscle from fat, so very muscular people may score as “overweight” while being healthy. It also doesn't apply to children and teens, who need age- and sex-specific charts.
Why use it?
- Works in kilograms or pounds.
- Shows the healthy weight range for your exact height.
- Explains what BMI can and can't tell you.
BMI categories for adults (WHO)
For a person 170 cm (5 ft 7 in) tall weighing 68 kg (150 lb), BMI is 68 ÷ 1.70² = 23.5 — in the healthy range. Their healthy weight range is about 53.5 to 72 kg.
| BMI | Category |
|---|---|
| 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 and above | Obesity class III |
The formula
Accuracy and limits
- This is a general estimate for healthy adults, not medical advice. Talk to a doctor or registered dietitian about your own situation.
- Some health bodies use lower cut-offs for people of South Asian, Chinese and other Asian backgrounds (for example, 23 for “overweight”), because health risks rise at lower BMIs.
Privacy
The calculation happens instantly in your browser. The numbers you enter are not sent to our servers or saved. There's no account to create and nothing to install.
Frequently asked questions
Is BMI accurate?
It's a useful screening tool across populations but a rough measure for individuals. Waist circumference and body fat percentage add useful context.
Does BMI work for children?
Not with adult categories. Children and teens use BMI-for-age percentiles from growth charts.
Last reviewed by the M2Toolkit team.