You should already know how to work out the interval (quality and number) between any two notes that are an octave apart or less. If you need to review that lesson first, go to Intervals Between Any Two Notes.
Intervals which are larger than one octave are called compound intervals. There are two ways to describe compound interval numbers:
- by the actual number of notes you count
- by using the word “compound”, plus the interval an octave lower.
You can use whichever you prefer.
Compound intervals need to be qualified (major, minor, perfect, diminished, augmented) in the same way as non-compound intervals.
Here is a compound interval:
There are 9 letter names between E and high F, so this a minor 9th.
Alternatively, you can call it a “compound minor 2nd”, because E to F is a minor second plus an octave.