A diminished triad contains a root, minor third and diminished fifth. The formula is 1–b3–b5. Written note names remain visible even when two names share the same piano key.
Root position and inversions
Each detail page keeps the same three chord tones across root position, first inversion and second inversion. The lowest chord tone changes while the chord root and written spelling stay the same.
Diminished triad, diminished seventh and half-diminished
A diminished triad has three notes: a root, minor third and diminished fifth (1–♭3–♭5), such as C–E♭–G♭. Adding a fourth note gives one of two seventh chords. A half-diminished seventh, written m7♭5 or ø7, adds a minor seventh (1–♭3–♭5–♭7): C–E♭–G♭–B♭. A fully diminished seventh, written dim7 or °7, adds a diminished seventh instead (1–♭3–♭5–𝄫7): C–E♭–G♭–B𝄫, where B𝄫 is played on the A key. This page lists the three-note triads; half-diminished chords have their own reference pages.