Semitone Ratio Interval Natural Half Step 0 1:1 unison 480 0 1 16:15 minor semitone 512 16:15 2 9:8 major second 540 135:128 3 6:5 minor third 576 16:15 4 5:4 major third 600 25:24 5 4:3 perfect fourth 640 16:15 6 45:32 diatonic tritone 675 135:128 7 3:2 perfect fifth 720 16:15 8 8:5 minor sixth 768 16:15 9 5:3 major sixth 800 25:24 10 9:5 minor seventh 864 27:25 11 15:8 major seventh 900 25:24 12 2:1 octave 960 16:15