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).

What key uses A diminished?

A° is the ii° of G minor and the vii° of B♭ major. Both keys share a two-flat signature.

How is A diminished different from A minor?

Only the fifth changes. A minor is A–C–E; A° is A–C–E♭. The half-step lower fifth is what creates the diminished tritone.

Where does A diminished appear in famous music?

Mozart's Symphony No. 40 in G minor uses A° at every cadence. Bach's B♭ major preludes use it as the standard leading-tone preparation. It's one of the most-played diminished triads in classical literature.

A diminished chord — notes, intervals, and practice

A diminished — A, C, E♭ — is the ii° of G minor and the vii° of B♭ major. The chord has one flat (E♭) on top of two naturals, a visual signature that makes it easy to recognise in flat-side scores.

Intervals

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

A→Cminor 3rd3 semitones
C→Ebminor 3rd3 semitones
A→Ebdiminished 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° has E♭ as the fifth, not E natural. Reading the fifth as E natural makes an A minor chord — same root, but a stable minor harmony rather than an unstable diminished one. In B♭ major literature, the E♭ is implicit in the key signature; on lead sheets the flat needs to be explicit.

In context

A° → D7 → G minor (ii° → V → i) is one of the most-used cadences in Baroque and Classical music in G minor — Mozart's G minor symphonies (No. 25 and No. 40) use this pattern repeatedly. In B♭ major, A° → B♭ caps phrases as the leading-tone cadence.

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).
What key uses A diminished?: A° is the ii° of G minor and the vii° of B♭ major. Both keys share a two-flat signature.
How is A diminished different from A minor?: Only the fifth changes. A minor is A–C–E; A° is A–C–E♭. The half-step lower fifth is what creates the diminished tritone.
Where does A diminished appear in famous music?: Mozart's Symphony No. 40 in G minor uses A° at every cadence. Bach's B♭ major preludes use it as the standard leading-tone preparation. It's one of the most-played diminished triads in classical literature.