Interval class

In music, specifically, musical set theory an interval class is an interval measured by the distance between its two pitch classes using integer notation. Created to account for octave and inversional equivalency, an interval class is the shortest distance possible between two pitches inverted so they are the closest possible. Since there are 12 pitch classes in the equal tempered scale the largest interval class is 6, since any interval larger than that comes closer to an octave of the other pitch.

For example, the interval of a perfect fifth, or 7, is 5.