Here's a quick guide. Once you've determined the size you find the quality. One way to do this is to count the number of half steps in the interval. 8 minor sixth 9 major sixth 10 minor seventh 11 major seventh 12 perfect octave. Intervals are subdivided into perfect and imperfect .
Perfect intervals are the unison, fourth, fifth, and octave.
When you alter a perfect interval by a half step the following chart applies diminished perfect augmented Imperfect intervals are the 2dn, 3rd, 6th, and 7th.