Dust and gas 90% radii of the IMTT disks (red) and Herbig disks (blue). The fitted relation between the two parameters is shown as the solid lines. The relationship is the same for both Herbig and IMTT disks. In yellow the region is shown where the difference between the dust and gas radii cannot be explained by optical depth effects only (Trapman et al. 2019). The dashed black line is a fit through the IMTT disks excluding SR 21, GW Ori, HT Lup, and SU Aur, as these have extended emission beyond the disk.