B♭ Diminished Chord (Bbdim, A#dim) on Piano
The Bbdim chord (Bb diminished) is built from 3 notes: Bb – Db – Fb. It is also written as A#dim.
Play these notes on a MIDI keyboard, your computer keyboard, or the on-screen keys and ChordKeys will name the chord back to you.
Notes and intervals
| Note | Degree | Interval from Bb | Semitones |
|---|---|---|---|
| Bb | 1 | root | 0 |
| Db | b3 | minor 3rd | 3 |
| Fb | b5 | diminished 5th | 6 |
Inversions
Rearranging which note sits at the bottom gives you 3 playable voicings of the same chord. Inversions let you move between chords with less hand movement.
| Voicing | Notes | Bass note |
|---|---|---|
| Root position | Bb – Db – Fb | Bb in the bass |
| 1st inversion | Db – Fb – Bb | Db in the bass |
| 2nd inversion | Fb – Bb – Db | Fb in the bass |
How the diminished chord is built
Every diminished chord uses the same interval formula: 1 (0 semitones), b3 (3 semitones), b5 (6 semitones). Starting on Bb and applying that formula produces Bb, Db, Fb. Learn the formula once and you can build a diminished chord on any of the twelve roots.
Keys that contain Bbdim
Every note of Bbdim belongs to these keys, so it will sit naturally in a progression written in any of them.
Other chords on Bb
Diminished chords on other roots
Frequently asked questions
What notes are in a Bbdim chord?
A Bbdim chord contains the notes Bb, Db, Fb. Those are the 1, b3, b5 degrees measured from the root note Bb.
How do you play Bbdim on piano?
Place your thumb on Bb, then add Db and Fb above it. With a right hand in root position the common fingering is 1–3–5.
Is Bbdim the same as A#dim?
Yes. Bbdim and A#dim are enharmonic equivalents — they sound identical and use the same piano keys. Which spelling you use depends on the key you are playing in.