The Formulas
Metric: BMI = weight(kg) / height(m)²
Imperial: BMI = 703 × weight(lb) / height(in)²
Imperial: BMI = 703 × weight(lb) / height(in)²
Common Mistakes
- Forgetting to square the height — a very common arithmetic slip that produces a nonsensical result.
- Using height in centimeters without converting to meters — always convert cm to m by dividing by 100 first.
- Treating BMI as a complete health diagnosis — it ignores muscle mass, bone density, age, and sex, all of which affect what a "healthy" number actually looks like for an individual.
Quick Reference
BMI Categories: Under 18.5 (Underweight) · 18.5–24.9 (Normal) · 25–29.9 (Overweight) · 30+ (Obese).
Frequently Asked Questions
Who created the BMI formula?
It was developed in the 1830s by Belgian mathematician Adolphe Quetelet as a population statistics tool — not as an individual health diagnostic, which is part of why it has well-known limitations today.
What should I use instead of BMI?
Body fat percentage, waist-to-hip ratio, or waist circumference alone often provide a more complete picture alongside BMI, rather than replacing it entirely.
