BMI

Definition

Body Mass Index (BMI) is calculated by dividing weight (kg) by the square of height (m²). It assesses weight status but does not distinguish fat mass from muscle mass.

How it works

BMI = weight (kg) / height² (m²). WHO classification: <18.5 underweight · 18.5-24.9 normal · 25-29.9 overweight · ≥30 obese. A muscular athlete may be in 'overweight' according to BMI.

Role

Rapid screening for weight-related risks in epidemiology and clinical practice.

Examples

• Man 80kg, 1.80m: BMI = 24.7 (normal)
• Woman 65kg, 1.60m: BMI = 25.4 (slight overweight)

Recommendations

Complement BMI with waist circumference measurement (metabolic risk if >88cm women, >102cm men).

Key takeaway

BMI is a screening tool, not a diagnosis — body composition is more informative.

Related terms