BMI Formula: How to Calculate Body Mass Index

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

BMI = kg / m²

Step‑by‑Step

1. Convert weight to kilograms (1 lb = 0.4536 kg).
2. Convert height to meters (1 in = 0.0254 m).
3. Square the height in meters.
4. Divide weight by squared height.

Example

70 kg, 1.75 m → 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.9 kg/m² (Normal weight).

Categories (Adults)

• Underweight: <18.5
• Normal: 18.5–24.9
• Overweight: 25–29.9
• Obesity: ≥30

For children, use age‑ and sex‑specific percentile charts.