log(R_s) vs. log(M_s) relation for all the samples under consideration. R_s is the half-mass radius and M_s the total stellar mass. Although R_s is not strictly identical to the effective radius R_e, they are very close to each other. Throughout this paper we always use R_s, which is easier to calculate for hydrodynamic models of galaxies, and assume R_s ≃ R_e. Burstein et al. (1997) sample: filled red circles are the ETGs, green open circles the SGs, blue filled triangles the DGs, filled red squares the GCs, and filled light-blue squares are the GCGs. The blue dashed line is the linear best fit of Eq. (2), i.e. log R_s = 0.60 log M_s − 5.859 relative to the sole ETGs, but extended to the regions of GCs and GCGs. Bernardi et al. (2010) sample: only ETGs are present, indicated by green filled circles. They fully overlap the ETGs of Burstein et al. (1997). The dashed magenta line is the linear best fit of the ETG data, but extended to GCs and GCGs. WINGS sample: dark-red filled circles are the ETGs, blue filled circles the BCGs, and the black filled circles are the GCGs. The olive-green dashed line is the linear best-fit of all WINGS objects together log R_s = 0.901log M_s − 9.245, but extended to DGs and GCs. Dwarf galaxies and Globular Clusters: coral filled circles are the DGs of Woo et al. (2008) and Geha et al. (2006) all together. Finally, the parallelogram shows the area occupied by the transition objects from GCs to DGs of Kissler-Patig et al. (2006).