How Do You Calculate Gain in Sinusoidal Signals?

[php]

how does one calculate a gain in signal e.g sine wave. do we take peak-to-peak (or peak) of the output divided by peak-to-peak(or peak) of the input?

 

[Fantasmagoria]

The ratio of the peak-to-peak voltages and RMS will be the same (both are related by the same factor of 1/sqrt2 if the signal is sinusoidal).
Gain is defined as 20dB*log(Vout/Vin)
Do you have a more specific question?