What is BMI?
BMI stands for Body Mass Index, a simple measurement that relates weight and height to indicate whether a person is underweight, at a normal weight, overweight, or obese. BMI is a simple screening measure that relates weight and height and can be useful for assessing weight status at the population level, precisely because it is easy to calculate and compare across populations.
BMI Formula
The formula is:
BMI = weight (kg) ÷ height (m)²
For example, a person weighing 70kg and measuring 1.70m in height has a BMI of 70 ÷ (1.70 × 1.70), resulting in approximately 24.2, which falls within the normal range.
BMI Categories Table
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25.0 to 29.9 | Overweight |
| 30.0 to 34.9 | Obesity Class I |
| 35.0 to 39.9 | Obesity Class II |
| 40.0 or higher | Obesity Class III |
Limitations of BMI
BMI is a population-level screening tool, not an individual diagnosis. It does not distinguish muscle mass from body fat, nor does it account for fat distribution, age, sex, or body composition. Someone with significant muscle mass may have a high BMI without having excess fat. Use the result as a starting point rather than a complete medical evaluation, and consult a healthcare provider for an individualized assessment.