• Adolescents;
  • anthropometry;
  • dual-emission X-ray absorptiometry;


What is already known about this subject

  • It is often not feasible to measure percent body fat using precise methods such as dual-emission X-ray absorptiometry (DXA).
  • Equations developed to estimate percent body fat in youth using measures that are feasible to collect in a variety of settings usually have been developed in focused samples and therefore have low generalizability.

What this study adds

  • First equations developed in a representative sample of American youth that estimate percent body fat using self-reported demographic variables as well as measured skin-folds and other anthropometric variables that are feasible to collect in a variety of settings.
  • Equations were demonstrated to have low levels of bias by BMI category and by race/ethnicity in non-Hispanic Whites, Mexican–Americans and African–Americans.


Percent body fat equations are usually developed in specific populations and have low generalizability.


To use a nationally representative sample of the American youth population (8–17 years old) from the 1999–2004 National Health and Nutrition Examination Survey data to develop gender-specific percent body fat equations.


Percent body fat equations were developed for girls and boys using information on weight, height, waist circumference, triceps skin-folds, age, race/ethnicity and menses status compared to dual-emission X-ray absorptiometry. Terms were selected using forward and backward selection in regression models in a 2/3 development sample and were cross-validated in the remaining sample. Final coefficients were estimated in the full sample.


Final equations included ten terms in girls and eight terms in boys including interactions with age and race/ethnicity. In the cross-validation sample, the adjusted R2 was 0.818 and the root mean squared error was 2.758 in girls. Comparable estimates in boys were 0.893 and 2.525. Systematic bias was not detected in the estimates by race/ethnicity or by body mass index categories.


Gender-specific percent body fat equations were developed in youth with a strong potential for generalizability and utilization by other investigators studying adiposity-related issues in youth.