What this BMI calculator does
This free body mass index calculator is a free bmi calculator tool that applies the bmi formula to your height and weight and gives a body mass index BMI number in plain language.
How to calculate BMI (and check it manually)
BMI is weight divided by height squared. We include how to calculate bmi manually so you can double-check. Results list bmi categories and a health risk assessment showing if you are overweight or obese or already in overweight and obesity.
Metric formula: BMI = weight (kg) / [height (m)]2. Imperial formula: BMI = (weight in pounds × 703) / (height in inches)2. Both give the same bmi calculation, just using different units.
Source: CDC BMI guidance
Body fat context
Because BMI does not measure fat directly, we add guidance on measuring body fat. Tracking body fat percentage (fat percentage) helps you spot low body fat or gains early and avoid overweight and obesity.
Limitations and next steps
BMI skips fat location and muscle, so athletes may score high and older adults may look normal when fat percentage rises. Pair it with waist size, movement, and a professional health risk assessment to keep health risks in perspective.