How many semitones is an Augmented Unison?

One semitone — C – C# — the same distance as a minor second, spelled differently. Count the semitones of any interval with the interval calculator.

Is an augmented unison the same as a minor second?

They sound identical in equal temperament. They are enharmonic, not equivalent: the augmented unison keeps the same letter name, the minor second moves to the next one.

When would I write an augmented unison?

Whenever a note is chromatically raised inside a line that stays on the same scale degree — a C natural moving to C♯ on its way to D.

How do I play Augmented Unison?

On guitar the handiest shape is Next string, G 5 · B 2, read as string and fret; the instrument panel draws it from any starting note with the other shapes. On the piano count 1 semitone up from any key, black keys included. Play the notes together for the harmonic form, one after the other for the melodic form.

Augmented Unison Interval: How It Sounds, with Song Examples

Play it on your instrument

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From

On the piano, from every note

From	Notes	Play it on your instrument
C	C – C#
C#	C# – C##
D	D – D#
Eb	Eb – E
E	E – E#
F	F – F#
F#	F# – F##
G	G – G#
Ab	Ab – A
A	A – A#
Bb	Bb – B
B	B – B#

Tap a key or a fret to hear it.

Number and quality

An interval has two names. The number counts the letter names from the lower note to the upper one, and the quality counts the semitones inside that number. Augmented Unison spans one letter name, which makes it a unison, and 1 semitone, which makes it augmented.

1 semitone

Read on: number and quality · half steps and whole steps · consonance and dissonance

Every unison

A unison can take these qualities, one semitone apart; choose one to see the upper note move and hear the pair.

Open Unison →

Where it lives

Augmented Unison is in every chord whose formula includes 1A from the root, in every scale that includes it from the tonic, and between these pairs of notes in a major key.

Related intervals

The intervals one step from Augmented Unison: its inversion, the same sound spelled differently, its simple or compound form, and its nearest neighbours in size.

Minor Second2m · 1 semitone · C – Db
The same sound, spelled differently
Unison1P · no semitones · C – C
One size away
Major Second2M · 2 semitones · C – D
One size away

Open it in a tool

Understanding Augmented Unison

Names and symbols

Augmented Unison is written A1, 1A: the letter is the quality, the number the size. Chord formulas on this site write the number first, as tonal does.

A unison is the interval of no distance, and it still has a quality: raise one of the two notes and it is an augmented unison, a chromatic half step that keeps its letter. A diminished second is the same distance written with two letters, C to D♭♭, which almost never happens outside theory exercises.

How it sounds

An augmented unison spans 1 semitone: C – C#. To the ear it is identical to a minor second, but the spelling says something different — the note has been chromatically altered rather than moved to the next letter.

Why the spelling matters

Notation follows function. A passing C♯ between C and D is an augmented unison, because the line is still on "C". Write it D♭ and you have claimed the note belongs to the D degree, which changes how a reader phrases and tunes it.

Learn this properly

Chapter 5: Intervals

Common questions

How many semitones is an Augmented Unison?: One semitone — C – C# — the same distance as a minor second, spelled differently. Count the semitones of any interval with the interval calculator.
Is an augmented unison the same as a minor second?: They sound identical in equal temperament. They are enharmonic, not equivalent: the augmented unison keeps the same letter name, the minor second moves to the next one.
When would I write an augmented unison?: Whenever a note is chromatically raised inside a line that stays on the same scale degree — a C natural moving to C♯ on its way to D.
How do I play Augmented Unison?: On guitar the handiest shape is Next string, G 5 · B 2, read as string and fret; the instrument panel draws it from any starting note with the other shapes. On the piano count 1 semitone up from any key, black keys included. Play the notes together for the harmonic form, one after the other for the melodic form.