Perfect fourth

This page is a stub. You can help the Xenharmonic Reference by expanding it.

The perfect fourth is the octave complement of the perfect fifth. It generally has a frequency ratio of 4/3, and is 498.0 cents in size when justly tuned.

While it has a relatively simple ratio (and can thus be used as a consonance especially in Pythagorean theory or as a harmonic interval), in classical theory, the perfect fourth above the root is often treated as a dissonance to resolve down to the major third.