# B♭ Half Diminished 7th piano chord (B♭m7♭5)

B♭m7♭5 contains B♭, D♭, F♭ and A♭. A diminished triad with the minor seventh added on top. B♭, D♭ and A♭ are black keys; F♭ is white.

- Canonical page: https://piano.org/chords/half-diminished/b-flat/
- Entity: chord:half-diminished-7th:b-flat
- Notes: B♭ D♭ F♭ A♭
- Formula: 1 ♭3 ♭5 ♭7
- Intervals from root: P1, m3, TT, m7
- Interval stack (semitones): 3 3 4
- Also written: B♭m7♭5, Bbm7b5, B♭ half diminished 7th
- 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 |
| ♭7 | A♭ | Minor seventh | 10 |

## Fingering

Rest your right hand over the notes with finger 2 on B♭, finger 3 on D♭, finger 4 on F♭, finger 5 on A♭. The left hand mirrors it.
Right hand 2-3-4-5, left hand 5-4-3-2. Source: piano.org fingering method v1.

## Inversions

| Position | Bass | Notes in order | Figured bass | Span |
| --- | --- | --- | --- | --- |
| Root position | B♭ | B♭3 D♭4 F♭4 A♭4 | 7 | 10 st, 138 mm |
| First inversion (B♭m7♭5/D♭) | D♭ | D♭4 F♭4 A♭4 B♭4 | 6/5 | 9 st, 124 mm |
| Second inversion (B♭m7♭5/F♭) | F♭ | F♭4 A♭4 B♭4 D♭5 | 4/3 | 9 st, 124 mm |
| Third inversion (B♭m7♭5/A♭) | A♭ | A♭4 B♭4 D♭5 F♭5 | 4/2 | 8 st, 110 mm |

## Voicings (10)

| Voicing | Notes | Span | Relation | Omits or adds |
| --- | --- | --- | --- | --- |
| Close, root position | B♭3 D♭4 F♭4 A♭4 | 10 st, 138 mm | identical | none |
| Close, first inversion | D♭4 F♭4 A♭4 B♭4 | 9 st, 124 mm | identical | none |
| Close, second inversion | F♭4 A♭4 B♭4 D♭5 | 9 st, 124 mm | identical | none |
| Close, third inversion | A♭4 B♭4 D♭5 F♭5 | 8 st, 110 mm | identical | none |
| Drop 2 | F♭3 B♭3 D♭4 A♭4 | 16 st, 220 mm | identical | none |
| Drop 3 | D♭3 B♭3 F♭4 A♭4 | 19 st, 261 mm | identical | none |
| Drop 2 and 4 | B♭2 F♭3 D♭4 A♭4 | 22 st, 303 mm | identical | none |
| Shell, root ♭7 ♭3 | B♭2 A♭3 D♭4 | 15 st, 206 mm | subset | omits F♭ |
| Guide tones, ♭3 and ♭7 | D♭4 A♭4 | 7 st, 96 mm | subset | omits B♭ and F♭ |
| Rootless close | D♭4 F♭4 A♭4 | 7 st, 96 mm | subset | omits B♭ |

## Diatonic function by key

| Key | Roman numeral | Function |
| --- | --- | --- |
| G♯ minor | iim7♭5 | Predominant |
| B major | viim7♭5 | Dominant function |

Classification system: common-practice functional harmony.

## Progressions (2)

| Progression | Key | Role | Sequence | Voice leading |
| --- | --- | --- | --- | --- |
| ii, v, i | G♯ minor | iim7♭5 | A♯m7♭5 to D♯m7 to G♯m7 | B♭m7♭5 opens the phrase |
| vii, I | B major | viim7♭5 | A♯m7♭5 to Bmaj7 | B♭m7♭5 opens the phrase |

## One-edit neighbors

| Becomes | Edit | Changes | Common tones |
| --- | --- | --- | --- |
| B♭dim | 1 ♭3 ♭5 | drops A♭ | 3 |
| B♭m7 | 1 ♭3 5 ♭7 | F♭ becomes F | 3 |
| B♭dim7 | 1 ♭3 ♭5 ♭♭7 | A♭ becomes A♭♭ | 3 |
| B♭m9 | 1 ♭3 5 ♭7 9 | F♭ becomes F, C | 3 |
| B♭m | 1 ♭3 5 | F♭, A♭ becomes F | 2 |
| B♭7 | 1 3 5 ♭7 | D♭, F♭ becomes D, F | 2 |
| B♭mMaj7 | 1 ♭3 5 7 | F♭, A♭ becomes F, A | 2 |
| B♭aug7 | 1 3 ♯5 ♭7 | D♭, F♭ becomes D, F♯ | 2 |
| B♭7sus4 | 1 4 5 ♭7 | D♭, F♭ becomes E♭, F | 2 |
| B♭m6 | 1 ♭3 5 6 | F♭, A♭ becomes F, G | 2 |

## Set theory

- Absolute pitch classes: {10, 1, 4, 8}
- Relative pitch classes: [0, 3, 6, 10]
- Normal order: [8, 10, 1, 4]
- Prime form: (0258)
- Forte number: 4-27
- Interval vector: <012111>

## 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 |
| A♭4 | 68 | 415.30 Hz |

## Questions and answers

### What notes are in B♭m7♭5?

B♭m7♭5 contains B♭, D♭, F♭ and A♭. The formula is 1, ♭3, ♭5, ♭7.

### How do you play B♭m7♭5 on piano?

Play B♭, D♭, F♭ and A♭ together. Right hand fingers 2, 3, 4, 5; left hand 5, 4, 3, 2. B♭, D♭ and A♭ are black keys; F♭ is white.

### What are the inversions of B♭m7♭5?

4 positions: root position B♭ D♭ F♭ A♭, B♭m7♭5/D♭, B♭m7♭5/F♭, B♭m7♭5/A♭.

### What keys contain B♭m7♭5?

2: iim7♭5 in G♯ minor, viim7♭5 in B major.

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

Drops A♭. 3 of the notes are shared.

### What is an easy B♭m7♭5 for small hands?

The guide tones, ♭3 and ♭7 voicing, D♭4 A♭4, spans 7 semitones or about 96 mm.

### What are the frequencies of B♭m7♭5?

From B♭3 at A440 in 12-TET: 233.08, 277.18, 329.63, 415.30 Hz.

### What is the set class of B♭m7♭5?

Prime form (0258), Forte 4-27, interval vector &lt;012111&gt;.

### How do I transpose B♭m7♭5 to another key?

Keep the 1, ♭3, ♭5, ♭7 formula on the new root. Cm7♭5 is C, E♭, G♭, B♭; C♯m7♭5 is C♯, E, G, B.

### Is A♯m7♭5 the same as B♭m7♭5?

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:half-diminished-7th:b-flat
Last reviewed: 2026-08-12