BMI Calculator
Enter your weight and height to calculate your Body Mass Index (BMI). Supports both metric (kg, cm) and imperial (lbs, ft/in) units. Results include your BMI category and a visual scale.
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What is BMI?
Body Mass Index (BMI) is a simple measurement that uses your height and weight to work out whether your weight is healthy. It was developed in the 19th century by Belgian mathematician Adolphe Quetelet and remains one of the most widely used screening tools in medicine.
BMI Formula
In imperial units: BMI = (weight in lbs × 703) ÷ height² (inches)
BMI Categories (WHO)
- Below 18.5 — Underweight
- 18.5 – 24.9 — Normal weight
- 25.0 – 29.9 — Overweight
- 30.0 – 34.9 — Obese (Class I)
- 35.0 – 39.9 — Obese (Class II)
- 40.0 and above — Obese (Class III / Severely obese)
Worked Examples
Example 1: Metric units
Weight: 75 kg | Height: 180 cm (1.80 m)
BMI = 75 ÷ (1.80 × 1.80) = 75 ÷ 3.24 = 23.1 — Normal weight
Example 2: Imperial units
Weight: 180 lbs | Height: 6'0" (72 inches)
BMI = (180 × 703) ÷ (72 × 72) = 126,540 ÷ 5,184 = 24.4 — Normal weight
Example 3: Overweight range
Weight: 90 kg | Height: 175 cm (1.75 m)
BMI = 90 ÷ (1.75 × 1.75) = 90 ÷ 3.0625 = 29.4 — Overweight
Limitations of BMI
BMI is a useful starting point but does not tell the whole story. It does not measure body fat directly and cannot distinguish between muscle and fat. A well-muscled athlete may show a "overweight" BMI despite very low body fat. Similarly, an older person may be in the "normal" range but have high body fat and low muscle mass.
For a full health assessment, consult a healthcare professional who can consider additional factors such as waist circumference, blood pressure, cholesterol, and lifestyle.