BMI Calculator for Metric and Imperial Units
Whether you measure your height in centimeters or feet and inches, and your weight in kilograms or pounds, this calculator provides seamless conversions between metric and imperial systems while maintaining exact mathematical equivalency.
How Is BMI Calculated?
BMI is calculated by dividing body mass by the square of body height. Depending on your preferred unit system, the formula is applied as follows:
Metric BMI Formula
To calculate in metric, convert height in centimeters to meters (divide by 100), square that value, and divide body weight in kilograms by the result.
Imperial BMI Formula
To calculate in imperial units, convert total height to inches, square that number, divide body weight in pounds by height in inches squared, and multiply by 703.
Adult BMI Categories
For adults and older teens, BMI values are grouped into standard categories established by public health agencies:
| BMI Range (kg/m²) | Category Label |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to less than 25 | Healthy weight |
| 25 to less than 30 | Overweight |
| 30 or higher | Obesity |
Healthy-Weight Range for Your Height
The standard BMI weight range for a given height represents the range of weights that correspond to a BMI of 18.5 to 24.9.
- Lower weight limit = 18.5 × [height in meters]²
- Upper weight limit = 24.9 × [height in meters]²
This range is based only on the standard BMI formula. It is not a personalized goal or medical recommendation.
BMI Limitations
While BMI serves as a convenient population screening metric, it has documented limitations when applied to individuals:
- Does Not Measure Body Composition: BMI cannot distinguish between muscle mass, bone density, and body fat.
- Athletes and Muscular Individuals: Individuals with significant muscle mass may record an elevated BMI without having high body fat.
- Older Adults: Older individuals may lose muscle mass and retain body fat, resulting in a normal BMI despite higher body fat levels.
- Not a Standalone Diagnostic Tool: BMI does not evaluate diet, physical activity, blood pressure, lipid profile, or metabolic health.
BMI for Children and Teenagers
This calculator supports adults and older teens aged 15 and above. Older teens (ages 15–19) can calculate their BMI with a teen disclaimer. For children under 15, BMI is interpreted using age- and sex-specific percentile growth charts.
Public Health Sources & Citations
- Centers for Disease Control and Prevention (CDC). About Adult BMI. Available at: cdc.gov/bmi/adult
- World Health Organization (WHO). Body Mass Index - BMI Classifications. Available at: who.int/fact-sheets