Body Mass Index (BMI) is the most widely used screening tool for weight categories. It's simple, fast, and free — but it's also frequently misunderstood.
The BMI Formula
In metric units, BMI = weight in kilograms ÷ (height in meters)². In imperial units, BMI = (weight in pounds ÷ (height in inches)²) × 703.
Understanding the Categories
- Underweight: BMI below 18.5
- Normal weight: BMI 18.5–24.9
- Overweight: BMI 25–29.9
- Obese: BMI 30 or higher
The Limitations of BMI
BMI doesn't distinguish between muscle and fat. A heavily muscled athlete can register as "overweight" or even "obese" despite having low body fat. It also doesn't account for fat distribution — visceral fat around the organs is more dangerous than subcutaneous fat.
For a more complete picture, pair BMI with a body fat percentage estimate and waist circumference. Use our BMI calculator and body fat calculator together for better insight.