It is also possible to calculate the RMS power of a signal. By analogy with RMS voltage and RMS current, RMS power is the square root of the mean of the square of the power over some specified time period. This quantity, which would be expressed in units of watts (RMS), has no physical significance. However, the term "RMS power" is sometimes used in the audio industry as a synonym for "mean power" or "average power". For a discussion of audio power measurements and their shortcomings, see [[Audio power]].
====Amplifier power efficiency====
The [[electrical efficiency]] of an [[electronic amplifier]] is the ratio of mean output power to mean input power. As discussed, if the output is resistive, the mean output power can be found using the RMS values of output current and voltage signals. However, the mean value of the current should be used to calculate the input power. That is, the power delivered by the amplifier supplied by constant [[voltage]] <math>V_{CC}</math> is
where <math>I_Q</math> is the amplifier's [[quiescent current|operating current]]. Clearly, because <math>V_{CC}</math> is constant, the time average of <math>P_\mathrm{input}</math> depends on the time ''average'' value of <math>I_\mathrm{out}</math> and not its RMS value. That is,
