More Information on BMI

David M. Garner, Ph.D.

The National Health and Nutrition Examination Survey III (NHANES III, Kuczmarski, Ogden, et al., 2002) has collected reference data to establish weight and height norms at different ages for girls/women and boys/men from birth to 20 years old. These norms indicate that BMI varies considerably with age and gender with children between 5 to 8 years old having the lowest BMI values followed by a steady increase with age. The expected changes in BMI associated females and males as “underweight” (BMI between the 5th and 10th percentile for girls/women and boys/men from 9 to 20 years old) and “very underweight” (BMI less than the 5th percentile). A BMI cutoff of between the 5th and 10th percentile for different ages and sexes should be used to determine if you meet the “underweight” BMI referral criterion for referral. For men and women 21 years old and older, the “underweight” category according to the NHLBI (1998) survey data were used to determine the “underweight” criterion for referral.

You can easily determine if you meet the BMI thresholds in Table 1 by finding your height on the column on the left in Table 2 and the BMI on the bottom and follow the height and the BMI columns to where the intersect. This is the weight that you need to be at or below for the BMI you have selected.

Although BMI is a convenient and useful weight classification tool, it does have limitations. For example, BMI can overestimate fatness for people who are athletic. Also, some races, ethnic groups, and nationalities have different body fat distributions and body compositions; therefore, the NHANES data are not appropriate for all groups (Kuczmarski, Ogden, et al., 2002).

Table 1: BMI Considered “Underweight” and “Very Underweight” Using Norms for Sex and Age

Data from the NHANES III survey, Kuczmarski, Ogden, et al., 2002.

Table 3

Table 2: Body Weight and Height to Calculate Body Mass Index (BMI)

Data from the NHANES III survey, Kuczmarski, Ogden, et al., 2002.

National Center for Health Statistics


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