Numerous upper bounds on the (anti)neutrino rest mass have been published based on the SN1987A observations. Here, we use a nonkinematic (thermal) time extent to provide a rest-mass estimate of a few eV (as mc2 energy), if not zero. In the solution, we find that a typical upper-bound formula for the mass implies that this thermal extent was attributable to about 10% of the particle energy measured on Earth. The present approach yields an expected value for the mass, given any theoretical or model-dependent estimate of the fraction of the detected neutrino energy attributable to the supernova temperature. This is a reposting of an old paper which describes an analysis protocol which can be applied for any supernova for which a population of neutrinos is observed.