BMI Calculator
How this BMI calculator works
This calculator computes your Body Mass Index (BMI) — a widely used screening measure that relates your weight to your height. Enter your height and weight, choose metric or imperial units, and the tool reports your BMI value, category, and the healthy weight range for your height.
The BMI formula
BMI = weight (kg) / height (m)²
For imperial units: BMI = 703 × weight (lb) / height (in)²
- Weight is your body mass in kilograms (or pounds)
- Height is converted to meters (or inches) before squaring
- The constant 703 converts the imperial result into the same scale
BMI categories
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
Healthy weight range
For your height, a BMI between 18.5 and 24.9 corresponds to a healthy weight range. This calculator multiplies your height (in meters) squared by 18.5 and 24.9 to show that range in kilograms. Staying within this range is associated with the lowest risk of weight-related health problems.
Limitations of BMI
- Athletes & muscular people — BMI may overestimate body fat because muscle weighs more than fat.
- Older adults — BMI may underestimate body fat because muscle mass declines with age.
- Children & teens — use age- and sex-specific percentile charts, not adult cutoffs.
- Pregnant or breastfeeding women — BMI does not apply; consult a healthcare provider.
- BMI does not measure body fat directly or account for fat distribution (e.g., abdominal fat).
BMI is a quick screening tool, not a diagnostic. For a full health assessment, talk to a healthcare professional who can consider body composition, waist circumference, and medical history.