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Calculating BMI With the English System and Understanding the Results

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.
 
For example: Weight = 150 lbs, Height = 5'5" (65 inches)
 
BMI calculation: [150 ÷ (65)2] x 703 = 24.96
 

Understanding the Results of BMI Calculation

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 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
 
It's important to remember that BMI is just one measure to assess the risk associated with weight.
 
(Click BMI and Weight for more information on other factors healthcare providers consider when determining risk for certain medical conditions related to weight.)
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