Body Mass Index (BMI) is a simple screening tool used to assess whether a person has a healthy body weight relative to their height. While not a perfect measure, it provides a useful starting point for health assessments.
How BMI Is Calculated
The BMI formula is straightforward:
BMI = weight (kg) / height (m)²
For imperial units:
BMI = (weight (lbs) × 703) / height (inches)²
BMI Categories
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased |
| 18.5 – 24.9 | Normal weight | Low |
| 25.0 – 29.9 | Overweight | Increased |
| 30.0 – 34.9 | Obese (Class I) | High |
| 35.0 – 39.9 | Obese (Class II) | Very High |
| 40.0+ | Obese (Class III) | Extremely High |
Limitations of BMI
BMI does not account for several important factors:
When to Use BMI
BMI is most useful as a population-level screening tool and a starting point for individual health conversations. It should always be combined with other measurements like waist circumference, body fat percentage, and clinical assessments.
Try It Yourself
Calculate your BMI instantly with our free BMI Calculator. Enter your weight and height to see your BMI category and health insights.