Calculating BMI

Body Mass Index (BMI) Calculation:

Body Mass Index (BMI)

BMI is calculated the same way for adults and children, based on the following formula:

Weight (in pounds)/(height [in inches])2 x 703 


For adults 20 and older, BMI is interpreted using standard weight status categories: 

BMI Weight Status
Below 18.5 Underweight
18.5 - 24.9 Normal/Healthy Weight
25-29.9 Overweight
30 and above Obese


For adolescents and children, however, BMI is interpreted differently, even though it is calculated using the same formula. Teens’ and children’s BMI need to be age- and sex-specific, because the amount of body fat changes with age and the amount of body fat differs between boys and girls. The CDC’s BMI-for-age growth charts take into account these differences and visually show BMI as a percentile ranking.   

For 2-year-olds through 19-year-olds, obesity is defined as at or above the 95th percentile of children of the same age and sex.  



BMI Chart for Boys: 



BMI Chart for Girls: 


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