Body Mass Index
Classifies weight status from height and weight using WHO body mass index bands.
Body mass index (BMI) relates weight to height and is the standard population measure of underweight, healthy weight, overweight and obesity as defined by the World Health Organization.
📐 Formula
BMI (kg/m²) = weight_kg / (height_m)²
🎯 When to Use
- Screening for underweight and obesity in adults.
- Contextualising imaging technique choices and radiation-dose considerations by body habitus.
- Risk stratification for weight-associated disease.
⚙️ How It Works
- Convert height from centimetres to metres.
- Divide weight in kilograms by the square of height in metres.
- Compare the result against WHO classification bands.
📊 Interpreting the Result
- <18.5 kg/m²: underweight.
- 18.5-24.9 kg/m²: normal (healthy) weight.
- 25.0-29.9 kg/m²: overweight.
- 30.0-34.9 obese class I; 35.0-39.9 class II; ≥40 class III.
⚠️ Limitations & Pitfalls
- Does not distinguish fat mass from lean mass; misclassifies muscular individuals.
- Population cut-offs differ for some Asian populations, where lower thresholds apply.
- Does not reflect fat distribution, which drives much cardiometabolic risk.
📚 References
- World Health Organization. Physical status: the use and interpretation of anthropometry. WHO Technical Report Series 854. Geneva: WHO; 1995.
- World Health Organization. Obesity: preventing and managing the global epidemic. WHO Technical Report Series 894. Geneva: WHO; 2000.
⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.