# What units are used for the Stefan-Boltzmann law?

I have a star with given temperature in Kelvin and radius in solar radii. I tried to calculate the luminosity of the star using Stefan Boltzmann's law, and got an absurd number (over 1 million). What am I doing wrong, and are there any units that I should use instead of Kelvin and solar units?

The Stefan-Boltzmann constant $$\sigma$$ is not a dimensionless quantity, it comes with units. So whatever units you use, you must ensure that the value you use for the Stefan-Boltzmann constant is consistent with them.
$$\sigma = 5.670\,374\,419\ldots \times 10^{-8}\,\rm W\,m^{-2}\,K^{-4}$$
you would either have to work with radius, luminosity and temperature in metres, watts and kelvins, or convert $$\sigma$$ to the units you are actually using.
For example, if you want to work in terms of solar radii and luminosities you have to account for the conversion factors $$L_\odot = 3.828 \times 10^{26}\,\rm W$$ and $$R_\odot = 6.957 \times 10^8\,\rm m$$, giving:
$$\sigma = 7.169\ldots \times 10^{-17}\ L_\odot\, R_\odot^{-2}\, \rm K^{-4}$$