Body mass index compares weight with height. The result helps identify a reference range, but it does not directly measure body fat or explain a person’s health on its own.
This calculator uses reference ranges for adults aged 20 and older. Children and teenagers need an assessment specific to age and sex.
How BMI is calculated
The calculation divides weight in kilograms by height in meters squared.
BMI = weight (kg) ÷ height² (m)
This page uses the following ranges:
| Result | Reference category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 to 34.9 | Class 1 obesity |
| 35 to 39.9 | Class 2 obesity |
| 40 or higher | Class 3 obesity |
What the result does not show
BMI does not distinguish between fat, muscle, and bone. It also does not show where fat is distributed. Health history, tests, blood pressure, body composition, and daily life can change the individual interpretation.
Use the result as an initial screening measure. Do not use the number to start diets, medication, or treatment on your own.
When to speak with a professional
Speak with a physician or dietitian if the result causes concern, if your weight changed significantly, or if you want to understand the result in the context of your health.
Sources
- World Health Organization: BMI and adult reference ranges
- CDC: adult BMI categories
- CDC: limits of BMI as an individual measure
This content is for information only. It does not replace diagnosis, treatment, or assessment by a healthcare professional.
