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.
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
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.