Calculating BMI

Most electronic health records (EHRs) automatically calculate body mass index (BMI) and BMI percentile for children when populated with age, sex, height, and weight. There are also tools such as CDC’s Child and Teen BMI Calculator that calculate children’s BMI metrics for parents, health care providers, and other users. To obtain correct calculations of BMI and BMI percentile, it is important to record accurate height and weight measurements.

Metric Formula
  • weight (kg) / [height (m)]2


  • [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. Since height is commonly measured in centimeters (cm), an alternate formula can be used—divide weight in kg by height in cm squared, and multiply the result by 10,000.

English Formula
  • weight (lb) / [height (in)]2 x 703

With the English system, weight in ounces (oz) must be changed to pounds (16 oz = 1 pound). Then, calculate BMI by dividing weight in pounds (lb) by height in inches (in) squared and multiplying by a conversion factor of 703.

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