Calculating BMI

What to know

Most electronic health records (EHRs) automatically calculate children's body mass index (BMI) and BMI percentile when populated with age, sex, height, and weight. CDC also offers a Child and Teen BMI Calculator to calculate metrics for children 2 years through 19. For correct calculations, record accurate height and weight measurements.

Medical professional sitting at a desk with a computer and a hand-held device.

BMI calculators

CDC's Child and Teen BMI Calculator calculates BMI, BMI percentile, and BMI category for children and adolescents 2 years through 19. The calculator also plots the result on CDC's growth charts, a useful resource for growth monitoring. For correct calculations, record accurate height and weight measurements.

For adults 20 and older, use CDC's Adult BMI Calculator. Both calculators use the formulas below to calculate BMI.

Metric

Formula in metric units‎

BMI = weight (kg) / [height (m)]2

or

BMI = [weight (kg) / height (cm) / height (cm)] x 10,000

With the metric system, the formula for BMI is weight in kilograms (kg) divided by height in meters (m) squared. Because height is commonly measured in centimeters (cm), you can use the alternate formula. The alternate formula is to divide weight in kg by height in cm squared and multiply the result by 10,000.

U.S. customary

Formula in U.S. customary units‎

BMI = weight (lb) / [height (in)]2 x 703

With the English system, change weight in ounces to pounds (16 ounces = 1 pound). Then, calculate BMI by dividing weight in pounds (lb) by height in inches (in) squared and multiply by 703.

CDC Growth Charts‎

A complete list of CDC's Growth Charts are available here.