What Is BMI?
Body Mass Index (BMI) is a numerical value calculated from your weight and height. It provides a simple screening measure to categorize individuals as underweight, normal weight, overweight, or obese. BMI was developed by Belgian mathematician Adolphe Quetelet in the 1830s.
BMI Formula
BMI = weight (kg) / height (m)2 Or in imperial units:
BMI = 703 × weight (lbs) / height (inches)2 BMI Categories
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 - 24.9 | Normal weight |
| 25.0 - 29.9 | Overweight |
| 30.0 - 34.9 | Obese (Class I) |
| 35.0 - 39.9 | Obese (Class II) |
| 40.0 and above | Obese (Class III) |
Limitations of BMI
While BMI is widely used, it has important limitations:
- Muscle vs. fat: Athletes and bodybuilders may have a high BMI due to muscle mass, not excess fat.
- Age: Older adults tend to have more body fat than younger adults at the same BMI.
- Sex: Women generally have more body fat than men at the same BMI.
- Body fat distribution: BMI does not account for where fat is stored. Abdominal fat is more dangerous than fat in other areas.
BMI should be used as a starting point, not a definitive measure of health. Consult a healthcare provider for a comprehensive health assessment.
Frequently Asked Questions
What is a healthy BMI range?
A healthy BMI is generally considered to be between 18.5 and 24.9. However, this range may vary by ethnicity and age. Some health organizations suggest lower cutoffs for Asian populations (23 for overweight, 27.5 for obese).
How accurate is BMI?
BMI is a useful screening tool for populations but has limitations for individuals. It does not measure body fat directly and cannot distinguish between muscle and fat. For a more accurate assessment, consider measurements like waist circumference, body fat percentage, or DEXA scans.