Here is Stefan-Boltzmann constant and its value is in FPS systems and in SI system. T is expressed in Rankin in FPS and in Kelvin in CGS systems. Most real bodies are not black, but they are selective absorbers and emitters. We define emissivity
Thus emissive power of any body
is Stefan-Boltzmann constant and its value is 
in FPS systems and 
in SI system. T is expressed in Rankin 
in FPS and in Kelvin 
in CGS systems.
