Watch the Major Scale Intervals online guitar lesson by Dave Celentano from CAGED Commander

The interval distance between any to notes can be measured in half step (one fret on guitar) and whole step (two frets) increments with a numeric name assigned to each. The interval from the first (root) to second note in the major scale is called a 'major 2nd' (whole step/two frets), first to third is a 'major 3rd' (two whole steps/four frets), first to fourth is a 'perfect 4th' (two and a half steps/five frets), first to fifth is a 'perfect 5th' (three and a half steps/seven frets), first to sixth is a 'major 6th' (four and a half steps/nine frets), first to seventh is a 'major 7th' (five and a half steps/eleven frets), and first to eighth (root) is an 'octave/perfect 8th' (six whole stepps/twelve frets). Here's a great ear training exercise - complete the assiciated melodies given for each interval (see attached charts).