Centers for Disease Control and Prevention




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

Calculating BMI
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6. Calculating BMI 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 (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.

 Bullet When using a hand-held calculator, if your calculator has a square function, divide weight (lbs) by height (in) squared, multiply by 703 and round to one decimal place.

 Bullet 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.

Calculations for BMI can be completed as a continuous equation. Note that the formula for the latter calculation is on the CDC Clinical Growth Charts and will be the calculation used in this module.


Example: 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 Using and interpreting the CDC Growth Charts, Step 4. Calculating BMI.

Calculator
 BMI web calculator

 


Flash calculator
(requires Flash 5
plug-in)

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?

Answer

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

Answer

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 is due to the conversion factor. 


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