Amplitude

Amplitude is the measure of the strength of a wave.

Since there are many types of wave, their amplitude has to be measured in different ways.

An abstract sine wave on a sheet of graph paper can be characterized by its maximum height above the x axis. The simplest, , has an amplitude of +/- 1. The class of "real" waves that are sine-like can be similarly measured, for instance, water waves on the ocean or a lake. It is important to differentiate between measuring the displacement from rest versus the peak-to-peak distance.

Sound waves can be expressed as a difference in pressure between their peak compressions and rarefactions, or, more practically, by their loudness or sound pressure level.