Adim piano chord, A diminished notes and fingering.

The Adim piano chord is A diminished: the notes A, C and Eb. It is two minor thirds stacked on top of each other. A up to C is three semitones, and C up to Eb is three more, so the fifth (Eb) is lowered to six semitones above the root. Chord charts write it as Adim or A°.

How to play Adim on piano

1. Find A on the keyboard. A is the white key between the second and third black keys of the group of three.
2. With your right hand, put finger 1 on A, finger 3 on C and finger 5 on Eb. Finger 1 is the thumb.
3. Press all three keys together. In root position they run from A3 to Eb4, a reach of 6 semitones. Play chord sounds them together and Arpeggio sounds them one by one, from the bottom up.
4. Click Left hand to see the left hand. It plays A2 to Eb3, one octave lower: A with finger 5, C with finger 3, Eb with finger 1.
5. The cards under the keyboard hold the three positions, with A, C and Eb at the bottom in turn. Play and Arpeggio on a card play that position.
6. Open Note names. As written the keys read A, C and Eb. Sharps shows A, C and D#, and Flats shows A, C and Eb. This chord is written with flats, so As written and Flats match.

How Adim is built

Counted from the root, the formula is 0, 3, 6. Stacked on each other the gaps are 3 + 3: two minor thirds. Compare it with A minor (A, C and E): the first two notes are the same, and the fifth is lowered one semitone from E to Eb. A perfect fifth is seven semitones; this one is six, and six semitones is a tritone.

Worked example: the pitch of A3. On a piano tuned to A4 = 440 Hz, a note 12 semitones below A4 has the frequency 440 × 2^(-12/12), which is about 220.00 Hz. C4 is 9 semitones below A4, so 440 × 2^(-9/12) gives about 261.63 Hz.

What the keys look like under your hand

A has a black key on each side, Ab on its left and Bb on its right. One of the three notes is a black key (Eb) and two are white keys (A and C). Your little finger plays Eb, a black key with D and E beside it. The little finger is short, so let the hand lean a little toward its edge and aim for the middle of the key.

Adim inversions and fingering

Adim has three positions. In root position A is at the bottom. In the first inversion, C is at the bottom and the chord is written Adim/C. In the second inversion, Eb is at the bottom and the chord is written Adim/Eb. The tightest reach, 6 semitones from the lowest key to the highest, is the root position. The widest, at 9, is the first inversion and second inversion.

The keys that hold Adim

Adim fits two of the major and natural minor keys that have a standard key signature, which means every note of it comes from that key's scale. The simplest is Bb major, with 2 flats, where it is chord vii°.

Progressions that use Adim, with the chord numbers and the chords in that key:

• Bb major: IV-vii°-iii-vi, which is Eb, Adim, Dm, Gm, a run of falling fifths.
• G minor: ii°-v-i, which is Adim, Dm, Gm, the minor ii-V-i, with the natural minor v.
• Bb major: vii°-I, which is Adim, Bb, the diminished chord leading up to the tonic.

Here is a worked example in Bb major. The chord before Adim in the first progression above is Eb (Eb, G and Bb). From Eb in root position, the closest way to reach Adim is its second inversion (Eb, A and C, lowest note first): one note stays where it is, and the others move 4 semitones in total, counting each note against the note in the same place from the bottom.

Adim also sits inside F7 (F, A, C and Eb): take the root off that dominant 7th and the notes left over are A, C and Eb.

What Adim sounds like

A diminished triad sounds tense and unresolved. It rarely sits still: the usual move is up a semitone to the chord built on Bb. It is used as a passing chord between two others and as a spice inside a progression.

Adim is the vii° chord in Bb major and the ii° chord in G minor. It is also chord vii° of Bb minor, using the raised seventh of the harmonic minor scale.

A common mistake with Adim

A common mistake is pressing E instead of Eb, one semitone higher than the fifth of Adim. That gives Am (A, C and E), a plain minor chord. The top key of Adim is a semitone lower than you might expect, so check it against the chord of the same root.

Chords to learn next

Chords close to Adim: A minor (raises the fifth; shares A and C); F7 (the dominant 7th it sits inside; contains all its notes); Bb major (the chord it leads to; shares no note); Am7 (adds a minor seventh to the minor chord; shares A and C).

Once Adim feels easy, play it and then Bb major to hear it resolve upward. For chords beyond these six types, and for guitar and ukulele shapes, use the chord finder. To play along with your computer keys, open the virtual piano. The piano chords page lists all 72 chords.