Text: Luigi Martino This shows one octave made up of semi-tones, but one can draw one for two octaves or more. The sharps and flats are grouped together. C Minor 2nd = 1 step past Major 2nd = 2 steps Minor 3rd = 3 steps Major 3rd = 4 steps 4th = 5 steps Diminished 5th (tri-tone) is 6 steps 5th = 7 steps Minor 6th = 8 steps Major 6th = 9 steps Minor 7th = 10 Major 7th = 11 steps Octave = 12 steps So you have an F to C. Start with F and move forward 7 steps. This will bring you to C. It is an interval of a 5th. Now work out the inversion of this relationship , C to F. Start with C and count the steps needed to arrive at F. There are 5 steps , so the inversion is a 4th. So one way it is a 5th and the other way it is a 4th. Add them together and they make 9.

See Also:

Source: