As used at astrophysics, Stefan's law is expressed as:
L = 4 π R2 σ Τ 4
L: Luminosity (in Watts)
R: Star radius
T: Star's surface temperature.
It's derived from the Stefan's formula, used priorly to calculate the star temperature:
j = 𝜎T4
where j is the Iradiance or Flux Density (Watt/m^2), which is estimated by comparisons with
references (like our Sun's Irradiance).
What do you think about the use of this formulae?
Here is a link about part of the topic.