The standard grips this chord is usually shown with.
C#dim7 is C#, E, G and Bb — C#dim with a diminished seventh stacked on top.
It sounds suspenseful and rootless. Three stacked minor thirds divide the octave evenly, so the same four notes spell four dim7 chords and the shape repeats every three frets.

| C# | E | G | Bb |
|---|---|---|---|
| 1 | ♭3 | ♭5 | ♭♭7 |
Leading-tone or passing chord — it can resolve almost anywhere.
Also written C#°7, C#o7 or C# diminished 7. The same chord either way; which spelling you meet depends on who wrote the chart.
C#dim7 in root position puts C# in the bass, which is the chord as it is spelled: the note it is named after underneath everything else.
4 of C#dim7’s 6 common shapes do this: x45353, 9x8989, 9-10-11-9-11-9, x-x-11-12-11-12.
Start with xx2323 — no barre and down at the nut. None of the shapes for C#dim7 uses an open string, so every one of them is movable; the lowest sits at the 2nd fret. 2 of the 6 need a barre. Together they cover the neck from the 2nd fret to the 12th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| xx2323 | 2nd fret | E, 1st inversion | G | all fretted |
| x45353 | 3rd fret | C#, root position | G | all fretted |
| xx5656 | 5th fret | G, 2nd inversion | Bb | all fretted |
| 9x8989 | 8th fret | C#, root position | C# | barred |
| 9-10-11-9-11-9 | 9th fret | C#, root position | C# | barred |
| x-x-11-12-11-12 | 11th fret | C#, root position | E | all fretted |
The same notes rebuilt from scratch give 5 shell, 14 drop 2, 10 drop 3 and 1 open string voicings, each on its own page.
Tensions. A shell of C#dim7, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (D#), the 11 (F#), the b13 (A) and the maj7 (B#).
A diminished seventh divides the octave evenly, so C#dim7 has no single root and no single destination: it can lead to F# or to D, and it is the same four notes either way.
Every note of C#dim7 is in C# diminished and C# half-whole diminished.
Change one note of C#dim7 and you have C#dim (drop the sixth), C#m6 (the flat fifth becomes a fifth), C#m7b5 (the sixth becomes a flat seventh) or C#mMaj7b5 (the sixth becomes a major seventh).
C#dim7 is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On C#dim7’s sound and use this page follows Stefan Kostka, Dorothy Payne & Byron Almén, Tonal Harmony (McGraw-Hill, 8th ed., 2018). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.