Intervals
Every interval within an octave, in ascending order — including both spellings of the tritone, which sound alike and behave differently. Each page gives the semitone count, the interval drawn on a chromatic ruler, keyboard and stave, its inversion, and the chords and scales it turns up in.
Within an octave
- Perfect unison0 semitones · C → C
- Minor second1 semitone · C → D♭
- Major second2 semitones · C → D
- Minor third3 semitones · C → E♭
- Major third4 semitones · C → E
- Perfect fourth5 semitones · C → F
- Augmented fourth6 semitones · C → F♯
- Diminished fifth6 semitones · C → G♭
- Perfect fifth7 semitones · C → G
- Minor sixth8 semitones · C → A♭
- Major sixth9 semitones · C → A
- Minor seventh10 semitones · C → B♭
- Major seventh11 semitones · C → B
- Perfect octave12 semitones · C → C
How interval names work
Every interval carries two labels. The number counts letter names inclusively — C to E covers C, D and E, so it is a third — and ignores sharps and flats entirely. The quality then pins down the exact size in semitones.
Which qualities are available depends on the number. Unisons, fourths, fifths and octaves are perfect and are never major or minor. Seconds, thirds, sixths and sevenths are major or minor and are never perfect. Any of them can be widened to augmented or narrowed to diminished.
| Number | Available qualities |
|---|---|
| Unison, 4th, 5th, octave | Diminished · Perfect · Augmented |
| 2nd, 3rd, 6th, 7th | Diminished · Minor · Major · Augmented |
This is why six semitones above C appears twice in the list above. Written as F♯ it spans four letters and is an augmented fourth; written as G♭ it spans five and is a diminished fifth. Identical in sound, different on paper, and they resolve in opposite directions.
What is an interval? works through both labels from scratch, and interval inversion explains why the list is really half as long as it looks.