  The flare produced when a star is tidally disrupted by a supermassive black
hole holds potential as a diagnostic of both the black hole mass and the star
mass. We propose a new method to realize this potential based upon a physical
model of optical/UV light production in which shocks near the apocenters of
debris orbits dissipate orbital energy, which is then radiated from that
region. Measurement of the optical/UV luminosity and color temperature at the
peak of the flare leads directly to the two masses. The black hole mass depends
mostly on the temperature observed at peak luminosity, while the mass of the
disrupted star depends mostly on the peak luminosity. We introduce {\sc
TDEmass}, a method to infer the black hole and stellar masses given these two
input quantities. Using {\sc TDEmass}, we find, for 21 well-measured events,
black hole masses between $5\times 10^5$ and $10^7 M_\odot$ and disrupted stars
with initial masses between 0.6 and $13M_\odot$. An open-source {\sc
python}-based tool for {\sc TDEmass} is available at
https://github.com/taehoryu/TDEmass.git.
