How to use the BMI Calculator
- Choose metric or US units.
- Enter your weight and height.
- See your BMI, category and the healthy weight range for your height.
- Optional: compare another weight at the same height; this is not a weight target.
BMI categories for adults
| 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 |
How BMI is calculated
BMI = weight (kg) ÷ height (m)². In US units: BMI = 703 × weight (lb) ÷ height (in)².
Limitations of BMI
BMI is a quick screening tool, not a diagnosis. It does not distinguish muscle from fat, so athletes may score as “overweight”, and it can underestimate risk in older adults. Some health bodies recommend lower cut-offs for people of South Asian, Chinese and other Asian backgrounds. Waist circumference is a useful extra check.
Frequently asked questions
Is BMI accurate for children?
No. Children and teens use BMI-for-age percentiles, which this calculator does not compute.
What is a healthy BMI?
For most adults, 18.5 to 24.9.