Body cell mass (BCM) is a valuable measure of functional nutritional status in children. As BCM is related to body size, it is essential that BCM is adjusted for stature when interpreting BCM data in children. Our aim was to examine the relationship between height and BCM in healthy children to determine the power by which height should be raised to adjust BCM for stature. This cross-sectional study calculated BCM by 40K counting in 146 healthy children aged between 5 and 18 years. The relationship between BCM and height was explored using log–log regression. The present results demonstrate that the power by which height should be raised to adjust for BCM in females is 2·39 (se 0·09) and for males is 2·92 (se 0·10). A simplified sex-specific version of the index, BCM/height2·5 for females and BCM/height3 for males, was found to be statistically valid and numerically convenient, with the proportion of variation that could be attributed to height being less than 2 %. The present study shows that there is a difference in the relationship between height and BCM for males and females and that BCM can be adjusted in children using the BCM index of BCM/height2·5 for females and BCM/height3 for males.