BMI Calculator
Body Mass Index (BMI) is weight in kilograms divided by height in meters squared. It is a simple screening tool used by health providers to categorize underweight, normal weight, overweight, and obesity. Enter your height and weight below; you can use metric or imperial units. This is not a diagnosis—see a doctor for health advice.
Calculate BMI
How it works
BMI = weight (kg) / height (m)². In imperial: weight in pounds ÷ (height in inches)² × 703. The result is a number; WHO categories are: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 and above obese.
Example: 70 kg and 1.70 m → BMI = 70 / (1.7×1.7) ≈ 24.2 (normal range).
When to use it
Use BMI as a quick screening reference. It does not replace a clinical assessment. Age, sex, muscle mass, and ethnicity can affect interpretation; children and pregnant women need different tools.
Frequently asked questions
- What is a healthy BMI range? WHO defines normal as 18.5–24.9. Under 18.5 is underweight; 25–29.9 overweight; 30+ obese. Ranges are for adults and do not account for muscle mass.
- Does BMI work for athletes? BMI does not distinguish muscle from fat. Very muscular people may be classed overweight. Use it as one indicator, not a sole measure of health.