Here are some great resources to help you learn and understand intervals:
Counting half-steps
Unison: 0
minor 2nd: 1
Major 2nd: 2
minor 3rd: 3
Major 3rd: 4
Perfect 4th: 5
Tritone: 6
Perfect 5th: 7
minor 6th: 8
Major 6th: 9
minor 7th: 10
Major 7th: 11
Octave (Perfect 8): 12
Diatonic (of the scale) intervals:
Major scale: Unison, M2, M3, P4, P5, M6, M7, P8
minor scale: Unison, M3, m3, P4, P5, m6, m7, P8
- http://www.practical-chords-and-harmony.com/intervals.html
- http://www.practical-chords-and-harmony.com/support-files/intervals.pdf
- http://www.eartraining-online.com/diatonic-intervals.html
Counting half-steps
Unison: 0
minor 2nd: 1
Major 2nd: 2
minor 3rd: 3
Major 3rd: 4
Perfect 4th: 5
Tritone: 6
Perfect 5th: 7
minor 6th: 8
Major 6th: 9
minor 7th: 10
Major 7th: 11
Octave (Perfect 8): 12
Diatonic (of the scale) intervals:
Major scale: Unison, M2, M3, P4, P5, M6, M7, P8
minor scale: Unison, M3, m3, P4, P5, m6, m7, P8