What is BMI?
BMI helps group adult results into standard reference categories. Healthcare professionals use it alongside other information rather than as a standalone measure of health or body fat.
How BMI is calculated
Metric formula
Example: 70 kg ÷ (1.75 × 1.75) = BMI 22.9.
US formula
The result is a number used with the adult ranges below.
Adult BMI ranges
These standard adult categories are used in guidance from the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC).
<18.5Healthy weight
18.5–24.9Overweight
25–29.9Obesity
≥30
| BMI | Category | Obesity class |
|---|---|---|
| Below 18.5 | Underweight | — |
| 18.5–24.9 | Healthy weight | — |
| 25.0–29.9 | Overweight | — |
| 30.0–34.9 | Obesity | Class 1 |
| 35.0–39.9 | Obesity | Class 2 |
| 40.0 or higher | Obesity | Class 3 |
Use BMI as one part of the picture
Why context matters
BMI does not distinguish muscle, bone, water, and fat. A muscular person may have a higher BMI without having excess body fat.
Other factors to consider
- Waist circumference and body composition
- Age, family history, and lifestyle
- Blood pressure, blood sugar, and overall health
Adult ranges should not be used for children or teenagers. For ages 2–19, BMI is interpreted using age- and sex-specific growth charts and percentiles.
When to seek guidance
Speak with a healthcare professional if you have concerns about your BMI, unexplained weight changes, or related health questions. They can interpret your result in context and suggest appropriate next steps.