Mathematics
BMI Calculator
Body Mass Index (BMI) is a simple screening index calculated from height and weight. It is used as a population-level indicator of underweight, healthy weight, overweight, and obesity, though it does not directly measure body fat and has known limitations for athletes and older adults. This calculator supports both metric and imperial inputs.
Calculator
Formula
Formula
BMI = weight(kg) / height(m)²
For metric: BMI = weight_kg / (height_cm / 100)². For imperial: first convert lb to kg (÷ 2.20462) and inches to cm (× 2.54), then apply the same formula. Healthy BMI range per WHO: 18.5–24.9 kg/m². Healthy weight range = [18.5 × height_m², 24.9 × height_m²].
Worked example
Person weighs 70 kg, height 175 cm. Calculate BMI.
- 1.Height in meters: 175 cm / 100 = 1.75 m
- 2.BMI = 70 / (1.75)² = 70 / 3.0625 = 22.86 kg/m²
- 3.Category: Normal weight (18.5–24.9)
- 4.Healthy weight range for 1.75 m: [18.5 × 3.0625, 24.9 × 3.0625] = [56.7 kg, 76.2 kg]
BMI = 22.86 (Normal weight). Healthy weight range: 56.7–76.2 kg.
Assumptions and limitations
- Uses WHO BMI categories: Underweight < 18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese ≥ 30.
- BMI is a population screening tool, not a direct measure of body fat or health.
- For athletes with high muscle mass, BMI may overestimate adiposity.
- Asian populations may use lower cutoffs (23 for overweight, 27.5 for obese) per WHO Asia-Pacific guidance.