Perfect fifth
The perfect fifth spans seven semitones with a just ratio of 3:2, an open, stable interval at the core of major and minor triads.
From C
- Size
- 7 semitones
- Abbreviation
- P5
- Just ratio
- 3:2 (701.96 cents)
- Equal-tempered
- 700 cents (−1.96 from just)
- Inversion
- Perfect fourth
What it sounds like
The perfect fifth is a perfect consonance, and its sound is open and stable. Its ratio, 3:2, is one of the simplest after the octave, so the two notes fuse easily and leave little beating. Melodically it is a clear leap with a sense of arrival, the kind used in opening calls and fanfares. Harmonically it is the outer interval of major and minor triads, which makes it the anchor of the triad. A fifth reads as stable in almost any context, though the third decides the chord's colour.
How to recognise it by ear
The first two different notes of 'Twinkle, Twinkle, Little Star' rise from C to G, a perfect fifth. Without that tune, use the sound of a root with its fifth, the open, hollow interval of a power chord, which sounds stable and complete. It forms the outer frame of every major and minor triad, so it is heard constantly in chordal music. Practice: play C and G together, then one after the other, and sing the leap back to the tonic until the open sound is automatic.
Theory
The perfect fifth inverts to the perfect fourth: the lower note moves up an octave, the semitones add to twelve, and the quality stays perfect. Major and minor triads contain a perfect fifth above the root, and dominant seventh and minor seventh chords include one as well. Its just ratio is 3:2, which measures 701.96 cents. The equal-tempered fifth is 700 cents, so the just size is 1.96 cents wider. Stacking twelve pure fifths overshoots seven octaves by the Pythagorean comma.
The perfect fifth above every note
Spelled by letter name, so the interval’s number is always right: a perfect fifth above E♭ is not the same spelling as above D♯.
| From | To | Hear it |
|---|---|---|
On the piano
Further reading
- Circle of Fifths Explained: Keys, Signatures, ChangesFundamentals · 6 min
- Pythagorean Tuning: How Stacked Pure Fifths Build a ScaleTuning & Temperament · 7 min
- Parallel Fifths and Octaves: Why the Rule ExistsCounterpoint · 7 min
Questions
Why is the perfect fifth called perfect?
The term describes a class of intervals with one fixed size: unison, fourth, fifth and octave. They have no major or minor form, only a perfect form, and altered versions are called diminished or augmented. The fifth's ratio of 3:2 is among the simplest in the system, which is one reason it was classed as perfect.
Is a perfect fifth the same as a power chord?
The interval is the same: two notes related by 3:2 and spanning seven semitones. The difference is context. A power chord is a root with a fifth and no third, so it has neither major nor minor colour. Adding a third turns it into a major or minor triad, and the third then defines the chord's character.
How do I tell a perfect fifth from a diminished fifth by ear?
Play the tonic, then the fifth, then the fifth lowered by a semitone. The perfect fifth sounds open and stable, while the diminished fifth sounds tense and hollow. Sing the top note first, then return to the tonic and listen for the pull before naming the interval.