ABSTRACTObjectivesTo establish age‐specific reference values for the arm span and arm span/height ratio of the Japanese population in children and adolescence and elucidate their characteristics compared with those of other populations.Study DesignWe analyzed data from a national survey on the body sizes of Japanese people conducted between 1992 and 1994 by the Research Institute of Human Engineering for Quality Life. This study was an observational cross‐sectional study, including 6089 boys and 4970 girls aged between 5.5 and 18.5 years. We constructed the reference values and delineated the reference curves for the arm span and arm span/height ratio of the Japanese population in childhood and adolescence using the LMS method. The references were compared with those of the Dutch and Turkish populations using the reference curve of 0 standard deviation.ResultsThe arm span of the Japanese population increased throughout childhood, with a particularly large increase at the age of puberty. The arm span/height ratio also increased slowly throughout childhood. The Japanese population had a smaller arm span/height ratio than the Dutch and Turkish populations of all ages in childhood and adolescence. Moreover, the arm span/height ratio of the Japanese population reached a constant value at an earlier age than in the Dutch and Turkish populations.ConclusionsWe constructed the first reference values for the arm span of Japanese children and adolescents. The Japanese population has shorter arm lengths in relation to their height, and their arm span/height ratio reaches a constant value at an earlier age, compared with the Dutch and Turkish populations.