Lesson 14 · All 12 keys

Diminished 7th Chord Trainer

Learn how a fully-diminished 7th chord is built one semitone-count at a time — three stacked minor 3rds — then put it to work with two MIDI exercises: playing all 12 diminished 7th chords around the circle of fourths, and a cadential I-V7-vii°7-I progression showing how it functions as a dominant substitute, in every key.

How a diminished 7th chord is built

A fully-diminished 7th chord is a 4-note chord built by stacking three identical minor 3rds on top of a root. Every diminished 7th chord — in any of the 12 keys — is built the exact same way, by counting semitones to the right from a root note:

  1. Start on the root — the note that names the chord.
  2. Count 3 semitones to the right to land on the minor 3rd.
  3. From there, count 3 more semitones to the right (6 semitones from the root) to land on the diminished 5th.
  4. From there, count 3 more semitones to the right (9 semitones from the root) to land on the diminished 7th.
Example — C diminished 7th (C°7): start on C, count 3 semitones right to reach E♭, 3 more to reach G♭, then 3 more to reach A (spelled B𝄫 in strict notation, but A on the keyboard). C‑E♭‑G♭‑A is the C°7 chord. The pattern 3, 3, 3 (9 semitones total from root to top) is what makes a chord "diminished 7th" — every one of the 12 diminished 7th chords is this same shape, just moved to start on a different key.
Because three stacked minor 3rds divide the octave into four perfectly equal parts, a diminished 7th chord is its own inversion: C‑E♭‑G♭‑A, E♭‑G♭‑A‑C, G♭‑A‑C‑E♭, and A‑C‑E♭‑G♭ are all built from the exact same four notes — there are really only 3 distinct diminished 7th chords in all of music, each one answering to 4 different "root" names depending on how it's spelled and where it resolves. That symmetry is also what gives it its restless, ambiguous sound: with no note anchoring it more than any other, it can resolve almost anywhere, which is exactly why composers use it as a pivot to slip between distant keys.

Try it: pick a root and build the chord step by step

Step 1 of 4
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Chord toneNoteSemitones from rootMIDI #

All 12 diminished 7th chords at a glance

ChordRoot+3 semitones → 3rd+3 semitones → dim 5th+3 semitones → dim 7th

This MIDI exercise plays all 12 diminished 7th chords, one after another, moving around the circle of fourths — each chord's root sits a perfect 4th (5 semitones) above the last one: C → F → B♭ → E♭ → A♭ → D♭ → G♭/F♯ → B → E → A → D → G → back to C. Every chord is played as a full 4-note diminished 7th (root, minor 3rd, diminished 5th, and diminished 7th together) — remember, because of the chord's symmetry, several of these 12 "roots" actually share the exact same four notes.

Chord 1 of 12
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The 12 chords, in circle-of-fourths order

#ChordRoot3rdDim 5thDim 7th

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Key of C
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Progression in C

DegreeChordNotes