Disk masses as function of the central object mass M_∗. Red dots and arrows are for the ρ Oph sample discussed in this paper. The black squares report the disk masses for BDs in Taurus from the F_{890 μm} detections: open, single-dish measurements from Andrews & Williams (2005); Broekhoven-Fiene et al. (2014); Mohanty et al. (2013); filled, from ALMA measurements by Ricci et al. (2014). Blue triangles show the values for the 7 BDs in Upper Sco observed with ALMA by van der Plas et al. (2016). For all objects, disk masses have been computed as in ρ Oph, assuming T = 25 (L_∗/L_⊙)^0.25 K, κ_{890 μm} = 2.0 cm²/g.