What Is BMI (Body Mass Index)?
Body Mass Index (BMI) is a simple calculation that uses your height and weight to estimate whether your weight falls within a healthy range. It’s a widely used screening tool used by doctors and health organizations worldwide, though it doesn’t directly measure body fat or account for muscle mass.
BMI Formula
Metric: BMI = weight (kg) ÷ [height (m)]²
Imperial: BMI = 703 × weight (lb) ÷ [height (in)]²
BMI Categories (WHO Standard)
- Below 18.5: Underweight
- 18.5 – 24.9: Normal weight
- 25 – 29.9: Overweight
- 30 and above: Obese
Limitations of BMI
BMI doesn’t distinguish between muscle and fat — so athletes and bodybuilders may show a higher BMI despite having low body fat. It also doesn’t account for age, sex, or body composition differences. Use it as a starting point, not a complete health assessment.
Frequently Asked Questions
Does the same BMI formula apply to children?
No. For children and teens, BMI is calculated using age- and sex-specific percentile charts rather than the fixed adult categories shown here.
Does a higher BMI always mean more body fat?
Not necessarily. Muscle is denser than fat, so athletic individuals can have a higher BMI even with low body fat percentage.
Should I rely on BMI alone to judge my health?
No. BMI works best alongside other measures like waist circumference, body fat percentage, and a doctor’s evaluation. This calculator provides an initial estimate, not medical advice.