If a star was marked with L/Teff in the Method column then its diameter was measured using the Stefan-Boltzmann Law. Stellar diameters are usually approximated using the Stefan–Boltzmann law with the star's luminosity and effective temperature. The Stefan-Boltzmann law describes how the temperature, luminosity, and volume of a star are all related in some way.
To calculate a star's diameter with the Stefan-Boltzmann law you must do the following calculation:
Square root of where represents the effective temperature in Kelvin (not Celsius) and represents the luminosity in terms greater than the Sun.