Chord · C# Diminished 7th
C♯dim7 Chord
C♯dim7 is C#, E, G and Bb — symmetrical; passes through every key. Used as a dominant substitute.
C♯dim7 on every instrument
The same 4 notes, 6 sets of hands. Open a diagram for alternate shapes, audio and the mistakes to avoid.
What C♯dim7 is made of
C# Diminished 7th (C# diminished 7th) is built from the notes C#, E, G, Bb, with the interval pattern 1, b3, b5, bb7. A common diminished 7th chord across many styles.
Stack 1, b3, b5 and bb7 on a root of C♯ and you get C#, E, G and Bb. That interval recipe is what makes the chord a diminished seventh chord — move the same shape to another root and the character travels with it, which is why Cdim7 sounds like a transposed C♯dim7.
Diminished 7th: Symmetrical; passes through every key. Used as a dominant substitute.
Spelling: the notes above are written the way a score would write them, not simplified to the nearest piano key. That is why this chord is spelled with C♯ rather than its enharmonic equivalent.
Keys that contain C♯dim7
No major or natural-minor key contains all 4 of these notes — this one gets borrowed.
Chords like this one sit outside the diatonic set — they arrive as secondary dominants, borrowed chords or passing harmony. Browse every key to see which progressions pull it in.
Other chords on C♯
Same root, different colour.
The same diminished seventh shape, moved
The identical interval recipe, built on other roots.
Questions people ask about C#dim7
- What notes are in the C#dim7 chord?
- C#dim7 is made of C#, E, G and Bb — the 1, b3, b5 and bb7 degrees of a diminished seventh chord built on C#.
- What keys use the C#dim7 chord?
- No major or natural-minor key contains all 4 notes of C#dim7. Chords like this arrive as borrowed harmony — secondary dominants, harmonic-minor colour, or chromatic passing chords — rather than as one of a key's native chords.
- How do you play C#dim7 on guitar and piano?
- This page shows C#dim7 on guitar, piano, ukulele, bass, mandolin and banjo — 9 voicings in total. Each diagram links to the full instrument page with alternate shapes, audio and common mistakes.
- Is C#dim7 the same as Dbdim7?
- Yes. C#dim7 and Dbdim7 are enharmonic — identical pitches written two different ways. Which spelling you use depends on the key you are in; C#dim7 is the spelling this site treats as canonical.
Learn the theory behind it
Why C♯dim7 behaves the way it does — the guides that explain the chord instead of just spelling it.