Peak-To-Peak Amplitude:

The peak-to-peak (pk-pk) amplitude of a wave is the net difference among the positive peak amplitude and the negative peak amplitude which is as shown below. The other way of saying this is that the pk-pk amplitude is equivalent to the positive peak amplitude plus the absolute value of the negative peak amplitude. The Peak to peak is a manner of expressing how much the wave level "swings" throughout the cycle.

Figure: Peak-to-peak amplitude.

In most of the waves, the pk-pk amplitude is twice the peak amplitude. This is the situation whenever the positive and negative peak amplitudes are similar.