What is BMI?
BMI is a numerical value calculated from a person's weight and height, used as a screening tool to categorize individuals into weight status categories such as underweight, normal weight, overweight, and obese.
Quick Facts
| Full Name | Body Mass Index |
|---|---|
| Created | 1832 by Adolphe Quetelet (Quetelet Index) |
| Specification | Official Specification |
How It Works
Body Mass Index is a simple calculation that divides a person's weight in kilograms by the square of their height in meters (kg/m²). Developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI provides a quick assessment of whether an individual's weight falls within a healthy range. The World Health Organization defines BMI categories as: underweight (<18.5), normal (18.5-24.9), overweight (25-29.9), and obese (≥30). While BMI is widely used due to its simplicity, it has limitations as it doesn't distinguish between muscle and fat mass, nor does it account for age, sex, ethnicity, or body composition.
Key Characteristics
- Formula: weight(kg) / height(m)²
- Imperial formula: (weight(lb) / height(in)²) × 703
- Underweight: BMI < 18.5
- Normal weight: BMI 18.5-24.9
- Overweight: BMI 25-29.9
- Obese: BMI ≥ 30
- Does not measure body fat directly
Common Use Cases
- Health screening and assessment
- Population health studies
- Insurance risk evaluation
- Fitness tracking applications
- Medical diagnosis support
Example
Loading code...Frequently Asked Questions
What is a healthy BMI range for adults?
A healthy BMI range for adults is typically between 18.5 and 24.9. A BMI below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above indicates obesity according to WHO standards.
Is BMI accurate for athletes and bodybuilders?
BMI is not accurate for athletes and bodybuilders because it doesn't distinguish between muscle and fat mass. Muscular individuals may have a high BMI but low body fat, making BMI misleading for assessing their health.
How do you calculate BMI using metric and imperial units?
For metric units, divide weight in kilograms by height in meters squared (kg/m²). For imperial units, divide weight in pounds by height in inches squared, then multiply by 703: (lb/in²) × 703.
Does BMI differ by age, gender, or ethnicity?
While the standard BMI formula is the same for everyone, interpretation may vary. Children use age-specific percentiles, and some health organizations recommend different thresholds for certain ethnic groups, particularly Asians.
What are the limitations of using BMI as a health indicator?
BMI limitations include: it doesn't measure body fat directly, doesn't account for muscle mass, bone density, or fat distribution, and doesn't consider age, sex, or ethnicity. It's a screening tool, not a diagnostic measure.