Diminished seventh chord: formula, notes and sound
A diminished 7th chord is three stacked minor thirds (0-3-6-9). Hear its dramatic sound, see it on every root, and learn why only three exist.
A diminished seventh chord stacks three minor thirds: root, minor third, diminished fifth and diminished seventh (0, 3, 6, 9 semitones). Bdim7 is B, D, F and A flat. Every note is 3 semitones from the next, so the chord is perfectly symmetrical and sounds dramatic and suspenseful.
Listen to Cdim7
C E♭ G♭ Bb♭
What is the formula of a diminished 7th chord?
| Chord tone | Interval from the root | Semitones | In C |
|---|---|---|---|
| Root | root | 0 | C |
| Third | minor third | 3 | E♭ |
| Fifth | diminished fifth | 6 | G♭ |
| Seventh | diminished seventh | 9 | B♭♭ |
Formula: 0-3-6-9 semitones. Written Cdim7, C°7.
What does a diminished 7th chord sound like?
Tense and theatrical: the sound of silent-film villains and dramatic classical passages. It can resolve in many directions.
How to recognise it by ear
- Symmetry check: all its notes are a minor third apart, so any note can sound like the root.
- Bdim7, Ddim7, Fdim7 and A♭dim7 use the same four keys, so there are only three different diminished seventh chords.
- It occurs on the 7th degree of the harmonic minor scale: G♯dim7 in A minor.
Quick test: is it a diminished 7th chord?
Four chords on different roots. Each is a diminished 7th chord or a chord it is often confused with.
Score: / 4 (your score updates as you answer)
Diminished 7th chords on all 12 roots
Spelled by letter from the formula, so thirds are always a letter apart (E♭, not D♯, in C minor).
| Chord | Notes | Hear it |
|---|---|---|
| Cdim7 | C E♭ G♭ Bb♭ | |
| C♯dim7 | C♯ E G B♭ | |
| Ddim7 | D F A♭ C♭ | |
| D♯dim7 | D♯ F♯ A C | |
| Edim7 | E G B♭ D♭ | |
| Fdim7 | F A♭ C♭ Eb♭ | |
| F♯dim7 | F♯ A C E♭ | |
| Gdim7 | G B♭ D♭ F♭ | |
| G♯dim7 | G♯ B D F | |
| Adim7 | A C E♭ G♭ | |
| A♯dim7 | A♯ C♯ E G | |
| Bdim7 | B D F A♭ |
Frequently asked questions
What notes are in a diminished seventh chord?
1, flat 3, flat 5, double flat 7. Bdim7 is B D F A flat; Cdim7 is C E flat G flat B double flat (played as A on a piano).
Why are there only three diminished seventh chords?
Each one divides the 12 semitones into four equal steps of 3. Starting a semitone higher gives a new one, but after three steps you are back to the same four keys: 12 / 4 = 3 distinct chords.
What is the difference between dim7 and half diminished?
The seventh. Dim7 has a diminished seventh (9 semitones above the root), half diminished has a minor seventh (10 semitones).
How is a diminished seventh chord written?
Cdim7 or C°7. On some charts "Cdim" also means the seventh chord, so check the context.