Histogram showing the disk sizes for disks around smooth single stars (from Long et al. 2019) and disks around the stars in multiple stellar systems. The black, red, and blue lines show the median of the distributions for smooth single disks, primaries, and secondaries, respectively. The radius of T Tau S, which is an unresolved binary (see Appendix A.1), is outside the plotted range. The two disks around primary stars with R_eff,dust > 40 au and R_disk,dust > 60 au show clear substructures in the dust distribution (CIDA 9A, UZ Tau E, Long et al. 2018). HK Tau B, an edge-on disk, also has R_disk,dust > 60 au. See text for discussion.