# A Diminished piano chord (Adim) Adim contains A, C and E♭. Two stacked minor thirds. E♭ is a black key; A and C are white. - Canonical page: https://piano.org/chords/diminished/a/ - Entity: chord:diminished:a - Notes: A C E♭ - Formula: 1 ♭3 ♭5 - Intervals from root: P1, m3, TT - Interval stack (semitones): 3 3 - Also written: Adim, Adim, A diminished - Parameters: A440, 12-TET, 165 mm octave, spans centre to centre ## Construction | Degree | Note | Interval from root | Semitones | | --- | --- | --- | --- | | 1 | A | Perfect unison | 0 | | ♭3 | C | Minor third | 3 | | ♭5 | E♭ | Tritone | 6 | ## Fingering Rest your right hand over the notes with finger 1 on A, finger 3 on C, finger 5 on E♭. The left hand mirrors it. Right hand 1-3-5, left hand 5-3-1. Source: piano.org fingering method v1. ## Inversions | Position | Bass | Notes in order | Figured bass | Span | | --- | --- | --- | --- | --- | | Root position | A | A3 C4 E♭4 | 5/3 | 6 st, 83 mm | | First inversion (Adim/C) | C | C4 E♭4 A4 | 6/3 | 9 st, 124 mm | | Second inversion (Adim/E♭) | E♭ | E♭4 A4 C5 | 6/4 | 9 st, 124 mm | ## Voicings (5) | Voicing | Notes | Span | Relation | Omits or adds | | --- | --- | --- | --- | --- | | Close, root position | A3 C4 E♭4 | 6 st, 83 mm | identical | none | | Close, first inversion | C4 E♭4 A4 | 9 st, 124 mm | identical | none | | Close, second inversion | E♭4 A4 C5 | 9 st, 124 mm | identical | none | | Open, fifth on top | A2 E♭3 C4 | 15 st, 206 mm | identical | none | | Root and third only | A3 C4 | 3 st, 41 mm | subset | omits E♭ | ## Diatonic function by key | Key | Roman numeral | Function | | --- | --- | --- | | G minor | ii° | Predominant | | B♭ major | vii° | Dominant function | Classification system: common-practice functional harmony. ## Progressions (2) | Progression | Key | Role | Sequence | Voice leading | | --- | --- | --- | --- | --- | | ii°, v, i | G minor | ii° | Adim to Dm to Gm | Adim opens the phrase | | vii°, I | B♭ major | vii° | Adim to B♭ | Adim opens the phrase | ## One-edit neighbors | Becomes | Edit | Changes | Common tones | | --- | --- | --- | --- | | Am7♭5 | 1 ♭3 ♭5 ♭7 | adds G | 3 | | Adim7 | 1 ♭3 ♭5 ♭♭7 | adds G♭ | 3 | | Am | 1 ♭3 5 | E♭ becomes E | 2 | | Am7 | 1 ♭3 5 ♭7 | E♭ becomes E, G | 2 | | AmMaj7 | 1 ♭3 5 7 | E♭ becomes E, G♯ | 2 | | Am6 | 1 ♭3 5 6 | E♭ becomes E, F♯ | 2 | | A | 1 3 5 | C, E♭ becomes C♯, E | 1 | | Aaug | 1 3 ♯5 | C, E♭ becomes C♯, E♯ | 1 | | Asus2 | 1 2 5 | C, E♭ becomes B, E | 1 | | Asus4 | 1 4 5 | C, E♭ becomes D, E | 1 | ## Set theory - Absolute pitch classes: {9, 0, 3} - Relative pitch classes: [0, 3, 6] - Normal order: [9, 0, 3] - Prime form: (036) - Forte number: 3-10 - Interval vector: <002001> ## Frequencies (close root position) | Note | MIDI | Frequency | | --- | --- | --- | | A3 | 57 | 220.00 Hz | | C4 | 60 | 261.63 Hz | | E♭4 | 63 | 311.13 Hz | ## Questions and answers ### What notes are in Adim? Adim contains A, C and E♭. The formula is 1, ♭3, ♭5. ### How do you play Adim on piano? Play A, C and E♭ together. Right hand fingers 1, 3, 5; left hand 5, 3, 1. E♭ is a black key; A and C are white. ### What are the inversions of Adim? 3 positions: root position A C E♭, Adim/C, Adim/E♭. ### What keys contain Adim? 2: ii° in G minor, vii° in B♭ major. ### What is the difference between Adim and Am7♭5? Adds G. 3 of the notes are shared. ### What is an easy Adim for small hands? The root and third only voicing, A3 C4, spans 3 semitones or about 41 mm. ### What are the frequencies of Adim? From A3 at A440 in 12-TET: 220.00, 261.63, 311.13 Hz. ### What is the set class of Adim? Prime form (036), Forte 3-10, interval vector <002001>. ### How do I transpose Adim to another key? Keep the 1, ♭3, ♭5 formula on the new root. Cdim is C, E♭, G♭; C♯dim is C♯, E, G. ## Provenance Every derived value above is computed by the piano.org theory kernel from the root, the quality and the stated parameters. Nothing is hand-entered per chord. Machine record: https://piano.org/api/knowledge/v1/entities/chord:diminished:a Last reviewed: 2026-08-12