The Mass from Luminosity calculator approximates the mass of a star based on its luminosity.
(L) This is the luminosity in Solar Units (i.e. multiples of luminosity compared to the Sun).
Stellar Mass (M): The calculator returns the mass of the star (M) in Solar Masses (multiples of the mass of the Sun). However, this can be automatically converted to other mass units via the pull-down menu.
The Math / Science
There is a relationship between mass and luminosity for stars in the "hydrogen" burning phase of their life cycle (the so called "main sequence"). This formula estimates the mass of a main sequence star given its luminosity.