Cdim piano chord, C diminished notes and fingering.

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

How to play Cdim on piano

1. Find C on the keyboard. C is the white key just left of the pair of black keys.
2. With your right hand, put finger 1 on C, finger 3 on Eb and finger 5 on Gb. Finger 1 is the thumb.
3. Press all three keys together. In root position they run from C4 to Gb4, 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 C3 to Gb3, one octave lower: C with finger 5, Eb with finger 3, Gb with finger 1.
5. The cards under the keyboard hold the three positions, with C, Eb and Gb at the bottom in turn. Play and Arpeggio on a card play that position.
6. Open Note names. As written the keys read C, Eb and Gb. Sharps shows C, D# and F#, and Flats shows C, Eb and Gb. This chord is written with flats, so As written and Flats match.

How Cdim 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 C minor (C, Eb and G): the first two notes are the same, and the fifth is lowered one semitone from G to Gb. A perfect fifth is seven semitones; this one is six, and six semitones is a tritone.

Worked example: the pitch of C4. On a piano tuned to A4 = 440 Hz, a note 9 semitones below A4 has the frequency 440 × 2^(-9/12), which is about 261.63 Hz. Eb4 is 6 semitones below A4, so 440 × 2^(-6/12) gives about 311.13 Hz.

What the keys look like under your hand

The black key nearest C is C# on its right. On its left there is none, because B and C are only a semitone apart. Two of the three notes are black keys (Eb and Gb) and one is a white key (C). Your little finger plays Gb, a black key with F and G 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. Finger 3 presses Eb, a black key between D and E. The middle fingers are the longest, so they reach black keys most easily.

Cdim inversions and fingering

Cdim has three positions. In root position C is at the bottom. In the first inversion, Eb is at the bottom and the chord is written Cdim/Eb. In the second inversion, Gb is at the bottom and the chord is written Cdim/Gb. 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 Cdim

Cdim 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 Db major, with 5 flats, where it is chord vii°.

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

• Db major: IV-vii°-iii-vi, which is Gb, Cdim, Fm, Bbm, a run of falling fifths.
• Bb minor: ii°-v-i, which is Cdim, Fm, Bbm, the minor ii-V-i, with the natural minor v.
• Db major: vii°-I, which is Cdim, Db, the diminished chord leading up to the tonic.

Here is a worked example in Db major. The chord before Cdim in the first progression above is Gb (Gb, Bb and Db). From Gb in root position, the closest way to reach Cdim is its second inversion (Gb, C and Eb, 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.

Cdim also sits inside Ab7 (Ab, C, Eb and Gb): take the root off that dominant 7th and the notes left over are C, Eb and Gb.

What Cdim 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 Db. It is used as a passing chord between two others and as a spice inside a progression.

Cdim is the vii° chord in Db major and the ii° chord in Bb minor.

A common mistake with Cdim

A common mistake is pressing G instead of Gb, one semitone higher than the fifth of Cdim. That gives Cm (C, Eb and G), a plain minor chord. The top key of Cdim 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 Cdim: C minor (raises the fifth; shares C and Eb); Ab7 (the dominant 7th it sits inside; contains all its notes); Db major (the chord it leads to; shares no note); Cm7 (adds a minor seventh to the minor chord; shares C and Eb).

Once Cdim feels easy, play it and then Db 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.