Interval Quality: Major, Minor & Perfect
An interval's number tells you how far apart two notes are on paper. Its quality tells you exactly how far apart they are in sound — and the rules depend on which family the number belongs to.
Number and quality are two separate labels
The number of an interval (2nd, 3rd, 4th...) just counts letter names from the bottom note to the top note — it says nothing about the exact size. The quality (major, minor, perfect, augmented, diminished) nails down the precise number of semitones. Together, "major 3rd" or "perfect 5th" fully describe an interval.
Two families, two rule sets
Every interval number belongs to one of two families, and each family has its own set of allowed qualities:
- The perfect family — unison, 4th, 5th, and octave. These can only be perfect, augmented, or diminished. "Major 4th" and "minor 5th" simply don't exist as labels.
- The major/minor family — 2nd, 3rd, 6th, and 7th. These can be major, minor, augmented, or diminished. The rule of thumb: shrink a major interval by one semitone and it becomes minor.
| Number | Family | Semitones |
|---|---|---|
| Unison | Perfect | 0 (Perfect) |
| 2nd | Major/minor | 1 (minor), 2 (Major) |
| 3rd | Major/minor | 3 (minor), 4 (Major) |
| 4th | Perfect | 5 (Perfect) |
| 5th | Perfect | 7 (Perfect) |
| 6th | Major/minor | 8 (minor), 9 (Major) |
| 7th | Major/minor | 10 (minor), 11 (Major) |
| Octave | Perfect | 12 (Perfect) |
Common questions
What's the difference between interval number and interval quality?
The number counts letter names between two notes. The quality describes the exact size in semitones for that number. You need both to fully name an interval.
Which intervals can be "perfect"?
Only the unison, 4th, 5th, and octave. They can be perfect, augmented, or diminished — never major or minor.
How do I convert a major interval to a minor one?
Shrink it by one semitone. The number stays the same; only the quality changes from major to minor.
Can a perfect interval be major or minor?
No — perfect-family intervals only ever take perfect, augmented, or diminished as labels.
Drill intervals until they're automatic
Melody Monkey's Ear Training tool quizzes you on number and quality together — free to try.
Open the ear trainer →Still stuck? Ask Your Personal Music Teacher about Interval Quality: Major, Minor & Perfect →