# B♭ Diminished piano chord (B♭dim)

B♭dim contains B♭, D♭ and F♭. Two stacked minor thirds. B♭ and D♭ are black keys; F♭ is white.

- Canonical page: https://piano.org/chords/diminished/b-flat/
- Entity: chord:diminished:b-flat
- Notes: B♭ D♭ F♭
- Formula: 1 ♭3 ♭5
- Intervals from root: P1, m3, TT
- Interval stack (semitones): 3 3
- Also written: B♭dim, Bbdim, B♭ diminished
- Parameters: A440, 12-TET, 165 mm octave, spans centre to centre

## Construction

| Degree | Note | Interval from root | Semitones |
| --- | --- | --- | --- |
| 1 | B♭ | Perfect unison | 0 |
| ♭3 | D♭ | Minor third | 3 |
| ♭5 | F♭ | Tritone | 6 |

## Fingering

Rest your right hand over the notes with finger 1 on B♭, finger 3 on D♭, finger 5 on F♭. The left hand mirrors it.
Right hand 1-3-5, left hand 5-3-1. Source: piano.org fingering method v1.

## Inversions

| Position | Bass | Notes in order | Figured bass | Span |
| --- | --- | --- | --- | --- |
| Root position | B♭ | B♭3 D♭4 F♭4 | 5/3 | 6 st, 83 mm |
| First inversion (B♭dim/D♭) | D♭ | D♭4 F♭4 B♭4 | 6/3 | 9 st, 124 mm |
| Second inversion (B♭dim/F♭) | F♭ | F♭4 B♭4 D♭5 | 6/4 | 9 st, 124 mm |

## Voicings (5)

| Voicing | Notes | Span | Relation | Omits or adds |
| --- | --- | --- | --- | --- |
| Close, root position | B♭3 D♭4 F♭4 | 6 st, 83 mm | identical | none |
| Close, first inversion | D♭4 F♭4 B♭4 | 9 st, 124 mm | identical | none |
| Close, second inversion | F♭4 B♭4 D♭5 | 9 st, 124 mm | identical | none |
| Open, fifth on top | B♭2 F♭3 D♭4 | 15 st, 206 mm | identical | none |
| Root and third only | B♭3 D♭4 | 3 st, 41 mm | subset | omits F♭ |

## Diatonic function by key

| Key | Roman numeral | Function |
| --- | --- | --- |
| G♯ minor | ii° | Predominant |
| B major | vii° | Dominant function |

Classification system: common-practice functional harmony.

## Progressions (2)

| Progression | Key | Role | Sequence | Voice leading |
| --- | --- | --- | --- | --- |
| ii°, v, i | G♯ minor | ii° | A♯dim to D♯m to G♯m | B♭dim opens the phrase |
| vii°, I | B major | vii° | A♯dim to B | B♭dim opens the phrase |

## One-edit neighbors

| Becomes | Edit | Changes | Common tones |
| --- | --- | --- | --- |
| B♭m7♭5 | 1 ♭3 ♭5 ♭7 | adds A♭ | 3 |
| B♭dim7 | 1 ♭3 ♭5 ♭♭7 | adds A♭♭ | 3 |
| B♭m | 1 ♭3 5 | F♭ becomes F | 2 |
| B♭m7 | 1 ♭3 5 ♭7 | F♭ becomes F, A♭ | 2 |
| B♭mMaj7 | 1 ♭3 5 7 | F♭ becomes F, A | 2 |
| B♭m6 | 1 ♭3 5 6 | F♭ becomes F, G | 2 |
| B♭ | 1 3 5 | D♭, F♭ becomes D, F | 1 |
| B♭aug | 1 3 ♯5 | D♭, F♭ becomes D, F♯ | 1 |
| B♭sus2 | 1 2 5 | D♭, F♭ becomes C, F | 1 |
| B♭sus4 | 1 4 5 | D♭, F♭ becomes E♭, F | 1 |

## Set theory

- Absolute pitch classes: {10, 1, 4}
- Relative pitch classes: [0, 3, 6]
- Normal order: [10, 1, 4]
- Prime form: (036)
- Forte number: 3-10
- Interval vector: <002001>

## Frequencies (close root position)

| Note | MIDI | Frequency |
| --- | --- | --- |
| B♭3 | 58 | 233.08 Hz |
| D♭4 | 61 | 277.18 Hz |
| F♭4 | 64 | 329.63 Hz |

## Questions and answers

### What notes are in B♭dim?

B♭dim contains B♭, D♭ and F♭. The formula is 1, ♭3, ♭5.

### How do you play B♭dim on piano?

Play B♭, D♭ and F♭ together. Right hand fingers 1, 3, 5; left hand 5, 3, 1. B♭ and D♭ are black keys; F♭ is white.

### What are the inversions of B♭dim?

3 positions: root position B♭ D♭ F♭, B♭dim/D♭, B♭dim/F♭.

### What keys contain B♭dim?

2: ii° in G♯ minor, vii° in B major.

### What is the difference between B♭dim and B♭m7♭5?

Adds A♭. 3 of the notes are shared.

### What is an easy B♭dim for small hands?

The root and third only voicing, B♭3 D♭4, spans 3 semitones or about 41 mm.

### What are the frequencies of B♭dim?

From B♭3 at A440 in 12-TET: 233.08, 277.18, 329.63 Hz.

### What is the set class of B♭dim?

Prime form (036), Forte 3-10, interval vector &lt;002001&gt;.

### How do I transpose B♭dim to another key?

Keep the 1, ♭3, ♭5 formula on the new root. Cdim is C, E♭, G♭; C♯dim is C♯, E, G.

### Is A♯dim the same as B♭dim?

Enharmonically yes: the same piano keys and the same sound, spelled differently.

## Provenance

Every derived value above is computed by the piano.org theory kernel from the root, the quality and the stated parameters. Nothing is hand-entered per chord.

Machine record: https://piano.org/api/knowledge/v1/entities/chord:diminished:b-flat
Last reviewed: 2026-08-12