Intervals
Octave
8P · 12 semitones
Twelve semitones — the same note, higher. The interval every tuning system in the world agrees on.
Also written P8 · 8P
Octave
8P · 12 semitones
On the piano, from every note
| From | Notes | Play it on your instrument |
|---|---|---|
| C | C – C | |
| C# | C# – C# | |
| D | D – D | |
| Eb | Eb – Eb | |
| E | E – E | |
| F | F – F | |
| F# | F# – F# | |
| G | G – G | |
| Ab | Ab – Ab | |
| A | A – A | |
| Bb | Bb – Bb | |
| B | B – B |
Tap a key or a fret to hear it.
Read on: number and quality · inversion · consonance and dissonance
Every octave
A octave can take these qualities, one semitone apart; choose one to see the upper note move and hear the pair.
Hear it in music
Songs that open with Octave: the first two notes of each are the interval, which is how most players learn to recognise it.
Somewhere Over the RainbowHarold Arlen
The opening "Some-where" leaps an octave.
Singin' in the RainNacio Herb Brown
The first two notes.
The Christmas SongMel Tormé
The opening interval.
Understanding Octave
Names and symbols
Octave is written P8, 8P: the letter is the quality, the number the size. Chord formulas on this site write the number first, as tonal does.
The octave is the one interval every tradition names the same way. An augmented seventh and a diminished ninth sound exactly like it and are written only when the spelling of a chord or a line demands them.
How it sounds
An octave spans 12 semitones: C – C. Its frequency ratio is exactly 2:1, the simplest possible, and the upper note reinforces the lower so completely that the ear treats them as the same pitch class with different heights.
This is why note names repeat. Octave equivalence is not a Western convention; it is close to a universal, and it is the reason a choir of men and women singing "the same note" are usually an octave apart without noticing.
How composers use it
Doubling a line at the octave is the standard way to add weight without adding harmony. Octave leaps in a melody read as dramatic precisely because they cost no harmonic change — the tension is purely in the distance.
Octaves also define register: the same chord voiced an octave lower can turn from clear to muddy, which is why arrangers think about spacing before they think about notes.
Learn this properly
Chapter 5: IntervalsCommon questions
- How many semitones is an Octave?
- An Octave spans 12 semitones: C – C. Count the semitones of any interval with the interval calculator.
- Why do notes repeat their names every octave?
- Because the 2:1 frequency ratio makes the upper note reinforce the lower so completely that the ear hears them as the same pitch class.
- What is the inversion of an octave?
- A unison. Invert an octave and both notes land on the same pitch.
- How do I play Octave?
- On guitar the handiest shape is Next string, B 1 · E 8, read as string and fret; the instrument panel draws it from any starting note with the other shapes. On the piano count 12 semitones up from any key, black keys included. Play the notes together for the harmonic form, one after the other for the melodic form.