How to Calculate BMI: Formula, Steps, and Interpretation

Body Mass Index (BMI) = weight (kg) ÷ [height (m)]².

Step-by-Step

1. Weight in kg: pounds ÷ 2.205.
2. Height in m: inches ÷ 39.37 (or cm ÷ 100).
3. Square height (m × m).
4. Divide weight by squared height.

Example

70 kg, 1.75 m → 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.9.

Classification (Adults)

• <18.5: Underweight
• 18.5–24.9: Normal
• 25–29.9: Overweight
• ≥30: Obesity (Class I 30–34.9, II 35–39.9, III ≥40)

Limitations

Does not distinguish muscle from fat; less accurate in athletes, elderly, pregnant women, and certain ethnicities. Use with waist circumference and clinical judgment.