What is a BMI calculator?
A BMI calculator uses your height and weight to calculate body mass index, or BMI. For adults, BMI is commonly used as a quick screening measure that places a height-to-weight result into a standard category: underweight, healthy weight, overweight, or obesity.
This calculator is designed for adults age 20 and older. You can enter U.S. customary measurements in feet, inches, and pounds, or use metric measurements in centimeters and kilograms. The result includes your BMI number, adult BMI category, and an approximate weight range corresponding to the standard healthy-BMI range for the height entered.
How does the BMI calculator work?
The calculator compares your weight with the square of your height. After you enter both measurements and select Calculate BMI, it applies the correct equation for the unit system you selected.
The result is rounded to one decimal place and matched with the standard adult BMI categories published by the Centers for Disease Control and Prevention (CDC). If the result is 30 or higher, the calculator also identifies the applicable obesity class.
The calculator does not estimate BMI while fields are half-completed. This helps prevent an unfinished entry from appearing as a final result.
What formula does the BMI calculator use?
BMI uses the same height-to-weight relationship in either measurement system. Only the unit conversion is different.
U.S. customary formula
Metric formula
For example, an adult who is 5 feet 9 inches tall and weighs 150 pounds has a BMI of about 22.1. The formulas used here follow the standard equations described by the CDC.
How do you use this BMI calculator?
- Choose U.S. Customary or Metric.
- Enter your height. Use feet and inches, or centimeters.
- Enter your weight. Use pounds or kilograms to match the selected unit system.
- Select Calculate BMI. Your BMI and adult category will appear in the result panel.
- Check the result. Review the BMI number, category, and healthy-BMI weight range shown for the entered height.
Use recent measurements when possible. Small height errors can noticeably change BMI because height is squared in the formula. Select Reset to clear all fields and start again.
What do BMI results mean?
For adults age 20 and older, BMI results are grouped into standard categories. The CDC currently lists the following adult ranges:
| BMI range | Adult category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 to 34.9 | Obesity — Class 1 |
| 35.0 to 39.9 | Obesity — Class 2 |
| 40.0 or greater | Obesity — Class 3 |
The healthy-BMI weight range shown by this tool is only the mathematical weight interval that corresponds to BMI 18.5 through 24.9 at the height entered. For a comparison of several height-based reference formulas, use the ideal weight calculator; neither result is a personalized medical recommendation.
What are the limitations of BMI?
BMI does not directly measure body fat or body composition. It cannot tell how much body weight comes from muscle, fat, bone, or body water. Because of this, two adults with the same BMI can have very different body compositions.
BMI also does not measure blood pressure, cholesterol, blood sugar, fitness, diet quality, or where body fat is distributed. A muscular person can have a relatively high BMI, while someone within the healthy-BMI category can still have other health risks.
The CDC describes BMI as a screening measure that should be considered with other factors when assessing an individual's health. For more context, see the NIH/NHLBI BMI resource.
Who should use this BMI calculator?
This calculator is intended for adults age 20 and older. It is useful for a quick educational BMI check, comparing U.S. and metric measurements, or verifying the math behind a BMI result.
It should not be used to interpret BMI for children or teenagers. For ages 2 through 19, the CDC uses sex-specific BMI-for-age percentiles because growth and body composition change with age. Use an appropriate child and teen BMI calculator instead.
This tool also does not replace individualized medical evaluation. If you have concerns about a major weight change, nutrition, pregnancy, an eating disorder, or another medical condition, a qualified health professional can provide context a general web calculator cannot.
Frequently asked questions about BMI
Sources and methodology
The formulas and adult category thresholds used by this calculator are based on current U.S. public-health guidance. These references are included so users can verify the method and read the original guidance.