Thanks for the quick response, this was perfect to help me with my understanding!I would think that's fine - all RMS is, for a pure sinusoid, is a scalar multiple (0.7071) of the "actual" voltage. So if you are consistent and used RMS for everything, you should be able to calculate impedance without issue. There's no "better" way to calculate the impedances, though - you can use RMS and normal voltage and current and get the same answer, as long as you don't mix them.