Weight Loss Home > Calculate Body Mass Index

English System
With the English system, the body mass index 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 BMI: Weight = 150 lbs, Height = 5'5" (65 inches)
BMI Calculation: [150 ÷ (65)2] x 703 = 24.96
 

Understanding the Results

For adults 20 years old 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 below:
 
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 BMI 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
 
Remember, BMI is just one measure to assess the health risks associated with being overweight or obese.
 
(Click BMI and Weight to learn more about other factors healthcare providers consider when determining risk for certain medical conditions related to weight.)
 
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
List of references (click here):
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