Scaling relation between luminosity, radius, velocity dispersion, virial mass, and CO-to-H₂ conversion factor for SMC clouds. In all panels, the dotted lines indicate the relations of Solomon et al. (1987), while gray shadows show the location of the outer Galaxy clouds (Heyer et al. 2001). In panels (a), (b), and (c) the dot-dashed lines display the best fit for the whole sample of the SMC (S/N > 5 and R > 2.2 pc). In panel (d), the median value of α_CO = 10.5 ± 5 M_⊙ (K kms⁻¹ pc²)⁻¹ for the SMC clouds obtained in this work is shown with a horizontal dashed line. The canonical conversion factor (α_CO = 4.36 M_⊙ (K kms⁻¹ pc²)⁻¹ ) for the Milky Way (MW in the panel) defined for clouds with L_CO = 10⁵ K kms⁻¹ pc² is also indicated with a horizontal dashed line.