Interval reference
Perfect fourth
4 letter names · 5 semitones · C → F
A perfect fourth spans 4 letter names and 5 semitones. Both halves of that description matter: the number comes from the letters, the quality from the exact size.
Starting on C, a perfect fourth reaches F. Its shorthand is P4, and traditionally it counts as consonant or dissonant depending on context.
How big it is
Hear it from any note
The explorer starts on C up to F. Play it one note after the other and then both together — the two ways a perfect fourth turns up in music — then change the bottom note: the distance stays the same while the spelling follows the letters.
Turned upside down
Move the lower note up an octave and a perfect fourth becomes a perfect fifth. The two numbers add up to nine, and the quality flips — major with minor, augmented with diminished, while perfect stays perfect.
Where you meet it
- The root to the fourth of a sus4 chord (C up to F in Csus4)
- Scale degrees 5 up to 8 (G up to C in C major)
From every starting note
| From | Up a perfect fourth |
|---|---|
| C | F |
| C♯ | F♯ |
| D | G |
| D♯ | G♯ |
| E | A |
| F | B♭ |
| F♯ | B |
| G | C |
| G♯ | C♯ |
| A | D |
| A♯ | D♯ |
| B | E |