BMI Calculator
Body mass index for adults age 20 and older, in metric or US units.
Adult BMI categories
| BMI | Weight status |
|---|---|
| Less than 18.5 | Underweight |
| 18.5 to less than 25 | Healthy weight |
| 25 to less than 30 | Overweight |
| 30 to less than 35 | Obesity (class 1) |
| 35 to less than 40 | Obesity (class 2) |
| 40 or greater | Obesity (class 3, severe) |
Categories as used by the US CDC for adults 20 and older.
Formula
- Metric: BMI = kg ÷ m²
- US: BMI = 703 × lb ÷ in²
Example: 70 kg and 1.75 m → 70 ÷ 3.0625 = 22.9. Need to convert weight first? lbs to kg.
FAQ
How is BMI calculated?
BMI = weight (kg) ÷ height (m)². In US units: BMI = 703 × weight (lb) ÷ height (in)².
What is a healthy BMI for adults?
The CDC classifies an adult BMI of 18.5 to less than 25 as healthy weight.
Does BMI work for children?
No. Children and teens (2–19) use BMI-for-age percentiles on growth charts, not these adult categories.
What are the limits of BMI?
BMI is a screening measure, not a diagnosis. It does not distinguish muscle from fat or account for body-fat distribution, age, sex or ethnicity. A healthcare provider can interpret it in context.
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