Perfect fifth interval

Perfect fifth in musical notationThe perfect fifth interval consists of two notes with seven semi-steps distance. For example, C to G note will result in this musical interval.

The reason for the name “perfect” goes back to the Medieval. The unison, fourth, fifth and octave were considered most consonant and therefore were given the name perfect. The perfect fifth interval is abbreviated P5 (an alternate spelling is diminished sixth).
Keyboard perfect fifth interval 
A perfect fifth C to G on the keyboard.

Listen to perfect fifth interval (C-G):

This interval is the same that consists in the 5th chords. For example, C5 with the notes C, G or D with the notes D, F#.

Ascending perfect fifth intervals

A list with ascending perfect fifth intervals:

Inversions of these intervals will result in perfect fourth intervals.

Descending perfect fifth intervals

A list with descending perfect fifth intervals:

See also the Circle of fifths.

Diminished fifth (tritone)

Diminished fifth in musical notationA related interval is the diminished fifth, or tritone (abbreviated TT). It includes one semi-step less than the perfect fifth interval. For example, C to Gb. The sound of the diminished fifth is dissonant and the interval is used in few chords, but can be found in diminished chords. For example, Cdim which is include C, Eb, Gb and Cdim7 which include C, Eb, Gb, A.

Listen to perfect fourth interval (C-Gb):

Keyboard diminished fifth interval 
A diminished fifth C to Gb on the keyboard.

Notice that the diminished fifth is identical with the augmented fourth.