Mass-size relation of star clusters measured at different scales. (a) Red, green, and blue pluses represent leaf clusters with effective radii R_eff, R_eff, 1, and R_eff, 2 defined in Sect. 3.3 and marked by colored ellipses in Fig. 1(a), respectively. (b) Magenta, cyan, and red pluses represent branch clusters, which are the subclusters in Table 1 of Kuhn et al. (2015b), and leaf clusters, respectively. k and r are the slope of the mass-size relation and the Pearson correlation coefficient, respectively.