Interval Number Names
Basic intervals are numbered from unison (one) up to an octave (eight).
You simply count the first note as “1” and then count each of the staff lines and spaces to the next note.
Interval number names are:
1 = Unison, 2 = Second, 3 = Third, 4=Fourth, 5=Fifth, 6 = Sixth, 7 = Seventh, 8 = Octave.
Compound intervals are musical intervals larger than an octave; 9th, 10th, 11th, 12th and 13th.