Chord · A Diminished 7th
Adim7 Chord
Adim7 is A, C, Eb and Gb — symmetrical; passes through every key. Used as a dominant substitute.
Adim7 on every instrument
The same 4 notes, 6 sets of hands. Open a diagram for alternate shapes, audio and the mistakes to avoid.
What Adim7 is made of
A Diminished 7th (A diminished 7th) is built from the notes A, C, Eb, Gb, with the interval pattern 1, b3, b5, bb7. A common diminished 7th chord across many styles.
Stack 1, b3, b5 and bb7 on a root of A and you get A, C, Eb and Gb. That interval recipe is what makes the chord a diminished seventh chord — move the same shape to another root and the character travels with it, which is why Cdim7 sounds like a transposed Adim7.
Diminished 7th: Symmetrical; passes through every key. Used as a dominant substitute.
Spelling: the notes above are written the way a score would write them, not simplified to the nearest piano key. That is why this chord is spelled with E♭ rather than its enharmonic equivalent.
Keys that contain Adim7
No major or natural-minor key contains all 4 of these notes — this one gets borrowed.
Chords like this one sit outside the diatonic set — they arrive as secondary dominants, borrowed chords or passing harmony. Browse every key to see which progressions pull it in.
Other chords on A
Same root, different colour.
The same diminished seventh shape, moved
The identical interval recipe, built on other roots.
Questions people ask about Adim7
- What notes are in the Adim7 chord?
- Adim7 is made of A, C, Eb and Gb — the 1, b3, b5 and bb7 degrees of a diminished seventh chord built on A.
- What keys use the Adim7 chord?
- No major or natural-minor key contains all 4 notes of Adim7. Chords like this arrive as borrowed harmony — secondary dominants, harmonic-minor colour, or chromatic passing chords — rather than as one of a key's native chords.
- How do you play Adim7 on guitar and piano?
- This page shows Adim7 on guitar, piano, ukulele, bass, mandolin and banjo — 8 voicings in total. Each diagram links to the full instrument page with alternate shapes, audio and common mistakes.
Learn the theory behind it
Why Adim7 behaves the way it does — the guides that explain the chord instead of just spelling it.