To calculate gain in sinusoidal signals, the output voltage (Vout) is divided by the input voltage (Vin), using either peak or peak-to-peak values. The gain can be expressed in decibels (dB) with the formula 20dB*log(Vout/Vin). Both peak-to-peak and RMS values yield the same gain ratio for sinusoidal signals, as they are related by a factor of 1/sqrt2. Understanding these calculations is essential for analyzing signal amplification. More specific questions can lead to deeper insights into gain calculations.