How to Calculate BMI and Interpret Results
Learn how to calculate your Body Mass Index (BMI), understand classification ranges, and discover why it is an important, though limited, tool for assessing your health.
Want to calculate now?
How to Calculate BMI and Interpret Results
What is BMI?
Body Mass Index (BMI) is an international measure adopted by the World Health Organization (WHO) to assess whether a person is at an ideal weight. It is a simple calculation relating an individual's weight and height to indicate if they are underweight, normal weight, overweight, or obese.
The BMI Formula
The calculation is very simple and can even be done without a calculator:
For example, if you weigh 70kg and are 1.75m tall:
- Multiply height by itself: 1.75 x 1.75 = 3.0625
- Divide weight by the result: 70 ÷ 3.0625 = 22.86
- The BMI is 22.86 kg/m²
BMI Classification Table
Reference values for adults (over 20 years old) are:
| BMI (kg/m²) | Classification |
|---|---|
| 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 more | Obesity Class III (Morbid) |
Limitations of BMI
While widely used, BMI is not a perfect measure of individual health. Its main limitations include:
- Muscle Mass: BMI does not distinguish between fat and muscle. Very muscular athletes may have a high BMI (indicating overweight) but low body fat percentage.
- Fat Distribution: It does not indicate where fat is stored. Visceral (abdominal) fat is more dangerous for cardiovascular health than fat on hips or legs.
- Age and Ethnicity: Ideal ranges may vary for the elderly or different ethnic groups.
Conclusion
BMI is an excellent initial screening tool. If your result is outside the normal range, consider it a signal to seek a more detailed professional evaluation, which may include skinfold measurements or bioimpedance.