Young circumstellar discs are made of almost invisible molecular hydrogen, making it extremely challenging to weigh it. Yet, the local mass determines the amount of material available for assembling planets and controls solid evolution by setting the strength of dust/gas coupling. When the disc-to-star mass ratio becomes of order ~0.1, the gravity of the disc may trigger gravitational instabilities that generates spirals inside the disc. Usual disc weighting by CO-isotopologues or dust remain uncertain since they rely on conversion factors and on the assumption that the disc is locally optically thin.
We propose a novel method for weighting massive discs. When high resolution kinematic data are available, we extract the velocity curve and fit it with an analytical model where both the disc and the star contributions are taken into account to obtain the disc mass (Veronesi et al. 2021, Lodato et al. 2023). We test and demonstrate the usefulness of the method by performing several SPH and radiative transfer simulations of self-gravitating protoplanetary discs with PHANTOM (Price et al. 2018) and MCFOST (Pinte et al. 2009), exploring a range of disc masses and cooling rates.