What notes are in an A♯ diminished chord?

A♯ diminished contains three notes: A♯ (the root), C♯ (the minor third), and E (the diminished fifth).

Is A♯ diminished the same as B♭ diminished?

Enharmonically yes — same three pitches. A♯° is the spelling inside B major; B♭° is the spelling inside C minor / D♭ major.

What key uses A♯ diminished?

A♯° is the vii° of B major and the ii° of G♯ minor. Both keys share the five-sharp signature.

When would I write A♯° instead of B♭°?

Whenever the surrounding harmony is in B major or G♯ minor — keeping the same accidental family avoids confusing key changes for the reader.

A# diminished chord — notes, intervals, and practice

A♯ diminished — A♯, C♯, E — is the vii° of B major and the ii° of G♯ minor. The chord uses two sharps (A♯, C♯) plus a natural fifth (E). It's rarer than its enharmonic neighbour B♭° because B major and G♯ minor are themselves less common keys, but the spelling is correct in those contexts.

Intervals

The A# diminished chord stacks two thirds on the root. Each interval and its size in semitones:

A#→C#minor 3rd3 semitones
C#→Eminor 3rd3 semitones
A#→Ediminished 5th6 semitones

On the keyboard

Each note of the A# diminished chord highlighted on a piano. Pitch class is what matters — any octave works.

On the guitar

One voicing of the A# diminished chord on a six-string guitar fretboard.

Common mistakes

A♯° pairs two sharps with a natural fifth — an unusual visual signature that beginners sometimes mis-spell as A♯-C♯-E♯ (which would make a different chord). The B-major key signature provides the sharps automatically; outside that context the chord is more often written as B♭° (Bb-Db-Fb), which uses the same pitches.

In context

A♯° → B major (vii° → I) is the cadence in B major. A♯° → D♯7 → G♯m (ii° → V → i) is the cadence in G♯ minor. The chord appears in Beethoven's late string quartets and Liszt's sharp-key piano writing.

Drill it

The A# diminished chord is one of 48 in the Chord Trainer. Open the full trainer to practice it alongside related chords with timing and best-time tracking.

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Frequently asked

What notes are in an A♯ diminished chord?: A♯ diminished contains three notes: A♯ (the root), C♯ (the minor third), and E (the diminished fifth).
Is A♯ diminished the same as B♭ diminished?: Enharmonically yes — same three pitches. A♯° is the spelling inside B major; B♭° is the spelling inside C minor / D♭ major.
What key uses A♯ diminished?: A♯° is the vii° of B major and the ii° of G♯ minor. Both keys share the five-sharp signature.
When would I write A♯° instead of B♭°?: Whenever the surrounding harmony is in B major or G♯ minor — keeping the same accidental family avoids confusing key changes for the reader.