A useful screening number, but not the whole health picture.
Body mass index compares weight with height. It is widely used as a simple adult screening measure because it is quick and consistent, but it does not directly measure body fat or diagnose any condition.
BMI formulas
Metric: weight in kilograms divided by height in metres squared.
Imperial: weight in pounds multiplied by 703, divided by height in inches squared.
Standard adult categories
| Category | BMI |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5–24.9 |
| Overweight | 25.0–29.9 |
| Obesity Class 1 | 30.0–34.9 |
| Obesity Class 2 | 35.0–39.9 |
| Obesity Class 3 | 40.0 or above |
What is BMI Prime?
BMI Prime is your BMI divided by 25. A value of 1.00 corresponds to the standard overweight threshold. It provides another way to understand how the score relates to that boundary.
When BMI can be misleading
- People with high muscle mass may have a high BMI without high body fat.
- BMI does not show where body fat is distributed.
- Pregnancy requires different assessment.
- Children and teenagers require age- and sex-specific percentiles.
- Risk may occur at lower BMI levels in some ethnic groups.