Perfect fourth
A perfect fourth is 5 half steps, written P4. From C it reaches F. Hear it one note after the other, then together.
What it sounds like
Five half steps. Open and strong, a little hollow when played together, and the interval between most neighbouring guitar strings.
Guitar tuning is built on it (E–A–D–G, then B–E). A sus4 chord replaces the third with a fourth, which wants to fall back.
How to recognise a perfect fourth by ear
Sing sol up to do, the classic pickup into a downbeat. It sounds like a call, open and a little formal. Played together it's hollow; guitarists hear it every time they tune two neighbouring strings.
Inside the C major scale, the perfect fourths are C–F, D–G, E–A, G–C, A–D and B–E. That's why it feels so ordinary: most neighbouring letters in a major key are this far apart.
Add an octave and a perfect fourth becomes a perfect eleventh (17 half steps), the 11 in m11 chords. Intervals bigger than an octave are called compound intervals; they keep the character of the smaller interval but sound more open.
Chords with a perfect fourth above the root, shown on C: Csus4.
A perfect fourth from every note
The letter name moves up 3 letters (a "fourth") and the distance is always 5 half steps.
| From | Up a perfect fourth | |
|---|---|---|
| C | F | |
| D♭ | G♭ | |
| D | G | |
| E♭ | A♭ | |
| E | A | |
| F | B♭ | |
| F♯ | B | |
| G | C | |
| A♭ | D♭ | |
| A | D | |
| B♭ | E♭ | |
| B | E |
Finding it on guitar
On one string, a perfect fourth is 5 frets up. Across to the next higher string it's the same fret (the strings are a perfect fourth apart, except G to B, where you add one fret). The diagram starts from A on the low E string.
Other intervals
- minor second
- major second
- minor third
- major third
- tritone
- perfect fifth
- minor sixth
- major sixth
- minor seventh
- major seventh
- octave
Perfect fourth: questions
How many half steps is a perfect fourth?
5. On the piano, count 5 keys up (black and white) from the starting note; on guitar, 5 frets up the same string.
What is a perfect fourth above C?
F. Above G it is C, above D it is G.
Is a perfect fourth consonant or dissonant?
Perfect consonance (treated as unstable over the bass). Five half steps.
What is the inversion of a perfect fourth?
A perfect fifth. Turn the interval upside down (put the lower note on top) and the two sizes always add up to 12 half steps: 5 + 7.
Spellings computed from letter names and half steps, and checked against both. Updated September 2026.