Sevenths
C diminished 7th chord
Symmetrical and very tense — every note is a minor 3rd apart.
Cdim7 is the vii°7 chord in C♯ minor.
- Notes
- CE♭G♭B𝄫
- Formula
- 1♭3♭5𝄫7
- Built from
- root · minor 3rd · diminished 5th · diminished 7th
How to play Cdim7
About the C diminished 7th chord
Playing it
There’s no open-string way to play Cdim7 on guitar with the root in the bass, so the standard shape is a barre across the 8th fret (8-9-10-8-10-8).
On piano, Cdim7 has two black keys (E♭ and G♭) and two white keys.
On ukulele the usual Cdim7 shape is 2323, using four fingers.
Related chords
Take away the root and the other three notes form E♭dim (E♭ G♭ B𝄫) — so you can think of Cdim7 as E♭dim with C added underneath.
Cdim7 is symmetrical — its notes are evenly spaced — so E♭dim7, F♯dim7 and Adim7 contain exactly the same notes. There are only three different-sounding diminished 7th chords in all.
Move a single note and Cdim7 becomes a different chord: drop the B𝄫 for Cdim, raise G♭ to G for Cm6 and raise B𝄫 to B♭ for Cm7♭5.
Where you’ll hear it
Notice the B𝄫 in Cdim7 (C E♭ G♭ B𝄫): each note of the chord takes its own letter (C–E–G–B), so the diminished 7th has to be written B𝄫 rather than A — the same key on a piano, spelled to fit the chord.
