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Training Module: Using the BMI-for-Age Growth Charts

Calculating BMI
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6. Calculating BMI by using the English system

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

Calculation: [weight (lb) / height (in) / height (in)] x 703

When using English measurements, ounces (oz) and fractions must be changed to decimal values. Then, calculate BMI by dividing weight in pounds (lb) by height in inches (in) squared and multiplying by a conversion factor of 703.

  • When using a handheld calculator, if your calculator has a square function, divide weight (lb) by height (in) squared, multiply by 703, and round to one decimal place.

  • If your calculator does not have a square function, divide weight by height twice, as shown in the calculation above, multiply by 703, and round to one decimal place. (Note that this formula is printed on the CDC Clinical Growth Charts, and it will be the calculation used in this module).

Let's calculate Sam's BMI using the English numeric system. His weight is 37 pounds and 4 ounces and his height is 41 1/2 inches.

Convert ounces and fractions to decimals:

  • Weight of 37 lbs and 4 oz = 37.25 lbs (16 ounces = 1 pound so 4 oz/16 oz = 0.25).
  • Height = 41.5 in.

(37.25 lbs / 41.5 in / 41.5 in) x 703 = 15.2

For more detailed instructions, see Use and Interpretation of the WHO and CDC Growth Charts for Children from Birth to 20 Years of Age in the United States.


BMI web calculator


Flash calculator
(requires Flash 5

Practice calculating BMI using the English system

Complete the following two calculations, rounding to one decimal place.

Calculation 1: Georgia's weight is 36 1/2 pounds and her height is 39 inches. What is Georgia's BMI?


Calculation 2: Jose's weight is 40 1/4 pounds and his height is 40 3/4 inches. What is Jose's BMI?


Note: There is a difference of 0.1 between BMI calculations when using the metric system (17.1) versus the English system (17.0). This difference is due to the rounding from two decimal places to one decimal place.

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