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Calculating BMI Using the English System and What the Numbers Mean

English System
If you're using the English system, the BMI formula is:

Weight in pounds (lbs) divided by height in inches (in) squared and multiplied by a conversion factor of 703 (weight (lbs) / [height (in)2] x 703).

Therefore, to calculate BMI, take the weight (lbs) and divide it by height (in). Take the result of that calculation and divide it by height again. Then, multiply that number by 703. Round to the second decimal place.

An example of calculating body mass index using the BMI formula:

Weight = 150 lbs
Height = 5'5" (65 inches)

BMI Calculation: [150 ÷ (65)2] x 703 = 24.96

What the Results Mean

For adults 20 years and older, the BMI results are interpreted using standard weight status categories that are the same for all ages and for both men and women. The standard weight status categories associated with BMI ranges for adults are shown in the following table.

 BMI Weight Status Below 18.5 Underweight 18.5 – 24.9 Normal 25.0 – 29.9 Overweight 30.0 and above Obese

For children and teens, after calculating the BMI, the number is plotted on the BMI-for-age growth charts (for either girls or boys) to obtain a percentile ranking. The percentile indicates the relative position of the child's BMI number among children of the same sex and age.

BMI-for-age weight status categories and the corresponding percentiles are shown in the following table.

 Weight Status Category Percentile Range Underweight Less than the 5th percentile Healthy weight 5th percentile up to the 84th percentile At risk of overweight 85th to less than the 95th percentile Overweight Equal to or greater than the 95th percentile

Keep in mind that BMI is just one measure to assess the risk associated with weight.

(Click BMI and Weight to learn more about other factors healthcare providers consider when determining risk for certain medical conditions related to weight.)

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