Notes and intervals
Perfect fourth
A perfect fourth is the interval of five semitones, as from C to F or E to A: it is the distance between almost every pair of neighbouring guitar strings.
What is a perfect fourth?
A perfect fourth is an interval of 5 semitones that spans four letter names: C, D, E, F. Examples: C-F, D-G, E-A, G-C, A-D, B-E.
It is the inversion of the perfect fifth: C up to G is a fifth, G up to the next C is a fourth. Together they make an octave (5 + 7 = 12 semitones). Going up a fourth or down a fifth lands on the same note name.
Why is the guitar tuned in fourths?
In standard tuning, E-A, A-D, D-G and B-E are all perfect fourths. Only the G-B pair is a major third. That is why the 5th-fret tuning method works: the 5th fret of the 6th string gives A, the open 5th string; the 5th fret of the 5th string gives D, and so on, except on the 3rd string, where you use the 4th fret to get B.
This layout puts four or five scale notes per string under your hand without shifting, which is what makes position playing possible. To see how other setups change these gaps, compare Drop D or DADGAD in the alternate tunings tool.
How do you play a perfect fourth on the fretboard?
- Next string, same fret: A at the 5th fret of the 6th string, D at the 5th fret of the 5th.
- From the 3rd to the 2nd string, one fret higher: open G, then C at the 1st fret of the 2nd string.
- Same string, 5 frets up: open low E, then A at the 5th fret.
So one finger flattened across two neighbouring strings gives you a fourth. Barre your index across strings 5, 4 and 3 at the 5th fret: D, G, C, two stacked fourths. This quartal voicing has no third, so it sounds open and modern, a staple of modal jazz and funk.
Example: sus4 chords and how they resolve
In a sus4 chord, the fourth replaces the third. Try these moves from folk and rock:
- D (xx0232) to Dsus4 (xx0233): on the 1st string, F# (2nd fret) rises to G (3rd fret) and comes back.
- A (x02220) to Asus4 (x02230): on the 2nd string, C# (2nd fret) rises to D (3rd fret).
The fourth creates a small tension that wants to fall back to the third. On the circle of fifths, moving counterclockwise means going up a fourth: C, F, B♭, E♭.
Key takeaways
- Perfect fourth = 5 semitones = same fret on the next string.
- The guitar is tuned in fourths, except G-B (a major third).
- The fourth is the inversion of the fifth: together they make an octave.
- It replaces the third in sus4 chords and stacks up in quartal voicings.
Frequently asked questions
Is a perfect fourth consonant or dissonant?
On its own it sounds stable and open. In classical harmony, though, a fourth above the bass is treated as a tension that needs to resolve, as in Dsus4 to D. It depends on where it sits in the chord.
How many frets is a perfect fourth?
Five on the same string, or the same fret on the next string up. The only exception is between the 3rd and 2nd strings, where you move up one fret.
Why not tune the whole guitar in fourths?
You can (E, A, D, G, C, F), and some jazz players do: every shape becomes identical on every string set. But common open chords become awkward, and the G-B major third in standard tuning is there precisely to keep them playable.
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.