How to Calculate BMI
The Body Mass Index (BMI) is a simple screening tool used to identify potential weight problems in adults. It is calculated by dividing a person's weight in kilograms by the square of their height in meters.
The BMI Formula
Depending on which measurement system you use, the formula varies slightly:
- Metric: BMI = weight (kg) / [height (m)]²
- Imperial: BMI = 703 × weight (lbs) / [height (in)]²
What Do the Numbers Mean?
According to standard health guidelines, BMI categories are defined as:
- Underweight: BMI less than 18.5
- Normal weight: BMI between 18.5 and 24.9
- Overweight: BMI between 25 and 29.9
- Obesity: BMI of 30 or greater
Limitations of BMI
While BMI is a useful starting point, it is not a perfect measure of health. It does not distinguish between muscle mass and fat mass. For example, athletes with high muscle mass may be classified as "overweight" despite having low body fat. It also does not account for age, sex, or fat distribution (visceral fat).
Frequently Asked Questions
Is BMI accurate for older adults? ▼
Older adults often have more body fat than younger adults with the same BMI. However, a slightly higher BMI in older age is sometimes associated with better survival rates.
What is a better alternative to BMI? ▼
The Waist-to-Hip Ratio (WHR) and Body Fat Percentage are often considered more accurate indicators of metabolic health than simple BMI.