Training your ear to identify musical intervals is one of the most important skills you can develop as a musician. This skill is called relative pitch as opposed to perfect pitch which is the identifying the actual pitch of a note.
Developing relative pitch allows you to understand the melodic and harmonic movement of a song. This is crucial to being able write your own music or play by ear. Unlike perfect pitch, which is most often acquired when one is very young, relative pitch is something that you can develop at any age.
This interactive diagram presents every musical interval up to a major 13th. The intervals of the Major scale (a.k.a. Diatonic scale) is the basis for all interval names and their distances. The scale degrees of the Diatonic scale make up the yardstick by which all musical intervals are measured. For an in depth discussion about this go to my article on intervals.
This diagram presents pitches that are an interval distance from C and only C. Here, C is our root note. Theoretically, this diagram could have been based on any of the notes of the Chromatic scale. This would have given us a new set of notes to compare but the thing about relative pitch is, that the intervals sound similar regardless of their root note. This means that the interval of a perfect fifth between C and G sounds like the perfect fifth between D and A.
Enharmonically equivalent notes refer to the same pitch and so the interval from the root to these notes sharing more than one name are the same.
Mouse over the notes on the musical staff, the scale degrees, or note names to activate a bar above the yardstick that indicates the selected interval and its name. To hear a specific interval, click on the play button below the musical staff. If the right end of the "interval bar" does not line up with your selected interval, move your cursor up or down from the play button.