What is Body Mass Index (BMI)?
Body Mass Index (BMI) is a screening metric established by the World Health Organization (WHO) that compares an individual's weight relative to their height. It serves as a practical, non-invasive method to classify adults into underweight, normal weight, overweight, and obesity categories.
How BMI Is Interpreted
For adults aged 20 and older, BMI values are grouped into the following international standard ranges:
- Underweight: BMI less than 18.5
- Normal weight: BMI between 18.5 and 24.9
- Overweight: BMI between 25.0 and 29.9
- Obesity Class I: BMI between 30.0 and 34.9
- Obesity Class II: BMI between 35.0 and 39.9
- Obesity Class III: BMI 40.0 or higher
How to Use This Calculator
Select your preferred measurement system (Metric or Imperial), enter your height and weight into the respective fields, and press Calculate Result. Your BMI and weight classification will appear instantly.
Mathematical Formula
Imperial: BMI = 703 × weight (lbs) / [height (inches)]²
Step-by-Step Worked Example
For an individual weighing 70 kilograms with a height of 1.75 meters (175 cm):
1. Square the height: 1.75 × 1.75 = 3.0625 m²
2. Divide weight by height squared: 70 / 3.0625 Ôëê 22.86
3. Result: A BMI of 22.9 indicates a Normal healthy weight range.
Important Considerations & Limitations
While BMI is an excellent general screening tool, it does not directly measure body fat percentage. It may overestimate body fat in athletes or individuals with significant muscular density, and underestimate body fat in elderly individuals who have lost muscle mass.
Authoritative References
World Health Organization (WHO) Technical Report Series: Physical Status - The Use and Interpretation of Anthropometry; National Institutes of Health (NIH) Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults.