Notes and intervals
Perfect fifth
A perfect fifth is the interval of seven semitones, as from C to G or A to E: the most stable interval after the octave, and with the root it forms a power chord.
What is a perfect fifth?
A perfect fifth is an interval of 7 semitones that spans five letter names: C, D, E, F, G. Examples: C-G, D-A, E-B, G-D, A-E, F-C. The one exception among natural notes is B-F, which is only 6 semitones: a diminished fifth.
The two frequencies sit in a 3 to 2 ratio, which explains its stability: after the octave, it is the most consonant interval. Its inversion is the perfect fourth.
How do you play a perfect fifth on guitar?
- Next string, two frets up: A at the 5th fret of the 6th string, E at the 7th fret of the 5th.
- From the 3rd to the 2nd string, three frets up: open G, then D at the 3rd fret of the 2nd string.
- String below, same fret: the fifth also sits an octave lower. For C at the 3rd fret of the 5th string, G is at the 3rd fret of the 6th.
That is exactly the power chord: root plus fifth, often with the octave on top. E5 is the open 6th string plus the 2nd fret of the 5th and 4th strings; G5 is the 3rd fret of the 6th string and the 5th fret of the 5th. With no third it is neither major nor minor, which is why it works so well with distortion.
The fifth in chords and keys
Every major and minor triad contains a perfect fifth: C, E, G and Am (A, C, E). A diminished chord lowers it (B, D, F), an augmented chord raises it (C, E, G#).
The fifth also organises keys. On the circle of fifths, each clockwise step goes up a fifth and adds a sharp: C (none), G (F#), D (F#, C#), A (three sharps). The interactive circle of fifths shows each key's signature, relative minor and chords.
Exercise: root-fifth alternating bass
This is the boom-chick of folk and country. For each chord, alternate the root and the fifth in the bass, with a strum in between:
- C: C (5th string, 3rd fret), strum, G (6th string, 3rd fret), strum.
- G: G (6th string, 3rd fret), strum, D (open 4th string), strum.
- D: D (open 4th string), strum, A (open 5th string), strum.
Loop C, G, D at 80 BPM. You get a complete bass line without changing any of your open chord shapes.
Key takeaways
- Perfect fifth = 7 semitones = two frets up on the next string (three between G and B).
- It is the most stable interval after the octave, a 3:2 ratio.
- Root + fifth = power chord.
- Neighbouring keys on the circle of fifths are a fifth apart.
Frequently asked questions
Why is it called a perfect fifth?
Because it has a single natural form with no major or minor version, like the fourth and the octave. A fifth one semitone smaller is diminished (C-G♭), one semitone larger is augmented (C-G#).
How do I tune with fifth harmonics?
The 7th-fret harmonic sounds a fifth (plus an octave) above the open string. The 5th-fret harmonic on the 6th string and the 7th-fret harmonic on the 5th string are both E: if they beat against each other, adjust the 5th string until the wobble disappears.
What is the fifth of each common chord?
C → G, D → A, E → B, F → C, G → D, A → E, B → F#. To find it on the neck, go up two frets on the next string. To check a full chord, use the chord identifier.
Related terms
Practise in the workshop
Take it from theory to the fretboard
Open the workshop tools and see this idea across the whole neck. Free account, no card needed.