I know that the ones with change in temperature don't matter since the increments are the same, but I'm not sure if I can memorize which ones require $K$ and which ones require $^{\circ}C$. Is it simpler than I think?
To clarify, I'm talking about formulas like Power for conductivity/radiation, dealing with ideal gases ($PV=nRT$), things like that.
Best Answer
You can always use Kelvin units for temperature. As far as I know there are no formulas which rely on Celcius units. You can use Celcius units for things like Newton's law of cooling which deal with the difference in temperatures. However, that is only because the difference between two temperatures in Celcius is the same as the difference in Kelvin. In short: always use Kelvin.