The properties of protostellar (Class 0/I) disks play an important role in planet formation by setting the environment for dust grain growth and the initial conditions for subsequent protoplanetary (Class II) disk evolution. However, obtaining these properties, especially the disk mass, has been challenging because translating observations of dust thermal emission to disk mass are subject to large uncertainties in dust optical depth and dust temperature.
In this talk I will present some new insights on the mass of typical protostellar disks through a synergy between theory and observation. Using the results from recent simulations, I will argue that the disk profile is regulated by several simple constraints, including that the disk should be marginally gravitationally unstable. Following these insights, I formulate a simple parametrized disk model that generates radial disk profiles as well as multi-wavelength mock observations of dust continuum emission. This model is then used to fit data from a recent observational survey of Orion protostellar disks. The majority of observed disks can be fit well by this model; moreover, the data are better fit by disk models assuming order-unity Q than those assuming larger Q values, suggesting that gravitational instability might indeed be common among protostellar disks. I use this model to produce new estimates of disk properties, and find that typical protostellar disks are significantly more massive than previously expected, with a typical disk-to-star mass ratio of order unity.