# B Diminished 7th piano chord (Bdim7)

Bdim7 contains B, D, F and A♭. Three stacked minor thirds. A♭ is a black key; B, D and F are white.

- Canonical page: https://piano.org/chords/diminished-7th/b/
- Entity: chord:diminished-7th:b
- Notes: B D F A♭
- Formula: 1 ♭3 ♭5 ♭♭7
- Intervals from root: P1, m3, TT, M6
- Interval stack (semitones): 3 3 3
- Also written: Bdim7, Bdim7, B 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♭ | Major sixth | 9 |

## Fingering

Rest your right hand over the notes with finger 1 on B, finger 2 on D, finger 3 on F, finger 5 on A♭. The left hand mirrors it.
Right hand 1-2-3-5, left hand 5-3-2-1. Source: piano.org fingering method v1.

## Inversions

| Position | Bass | Notes in order | Figured bass | Span |
| --- | --- | --- | --- | --- |
| Root position | B | B3 D4 F4 A♭4 | 7 | 9 st, 124 mm |
| First inversion (Bdim7/D) | D | D4 F4 A♭4 B4 | 6/5 | 9 st, 124 mm |
| Second inversion (Bdim7/F) | F | F4 A♭4 B4 D5 | 4/3 | 9 st, 124 mm |
| Third inversion (Bdim7/A♭) | A♭ | A♭4 B4 D5 F5 | 4/2 | 9 st, 124 mm |

## Voicings (10)

| Voicing | Notes | Span | Relation | Omits or adds |
| --- | --- | --- | --- | --- |
| Close, root position | B3 D4 F4 A♭4 | 9 st, 124 mm | identical | none |
| Close, first inversion | D4 F4 A♭4 B4 | 9 st, 124 mm | identical | none |
| Close, second inversion | F4 A♭4 B4 D5 | 9 st, 124 mm | identical | none |
| Close, third inversion | A♭4 B4 D5 F5 | 9 st, 124 mm | identical | none |
| Drop 2 | F3 B3 D4 A♭4 | 15 st, 206 mm | identical | none |
| Drop 3 | D3 B3 F4 A♭4 | 18 st, 248 mm | identical | none |
| Drop 2 and 4 | B2 F3 D4 A♭4 | 21 st, 289 mm | identical | none |
| Shell, root ♭♭7 ♭3 | B2 A♭3 D4 | 15 st, 206 mm | subset | omits F |
| Guide tones, ♭3 and ♭♭7 | D4 A♭4 | 6 st, 83 mm | subset | omits B and F |
| Rootless close | D4 F4 A♭4 | 6 st, 83 mm | subset | omits B |

## One-edit neighbors

| Becomes | Edit | Changes | Common tones |
| --- | --- | --- | --- |
| Bdim | 1 ♭3 ♭5 | drops A♭ | 3 |
| Bm7♭5 | 1 ♭3 ♭5 ♭7 | A♭ becomes A | 3 |
| Bm6 | 1 ♭3 5 6 | F becomes F♯ | 3 |
| Bm | 1 ♭3 5 | F, A♭ becomes F♯ | 2 |
| Bm7 | 1 ♭3 5 ♭7 | F, A♭ becomes F♯, A | 2 |
| BmMaj7 | 1 ♭3 5 7 | F, A♭ becomes F♯, A♯ | 2 |
| B6 | 1 3 5 6 | D, F becomes D♯, F♯ | 2 |

## Set theory

- Absolute pitch classes: {11, 2, 5, 8}
- Relative pitch classes: [0, 3, 6, 9]
- Normal order: [2, 5, 8, 11]
- Prime form: (0369)
- Forte number: 4-28
- Interval vector: <004002>

## Frequencies (close root position)

| Note | MIDI | Frequency |
| --- | --- | --- |
| B3 | 59 | 246.94 Hz |
| D4 | 62 | 293.66 Hz |
| F4 | 65 | 349.23 Hz |
| A♭4 | 68 | 415.30 Hz |

## Questions and answers

### What notes are in Bdim7?

Bdim7 contains B, D, F and A♭. The formula is 1, ♭3, ♭5, ♭♭7.

### How do you play Bdim7 on piano?

Play B, D, F and A♭ together. Right hand fingers 1, 2, 3, 5; left hand 5, 3, 2, 1. A♭ is a black key; B, D and F are white.

### What are the inversions of Bdim7?

4 positions: root position B D F A♭, Bdim7/D, Bdim7/F, Bdim7/A♭.

### What is the difference between Bdim7 and Bdim?

Drops A♭. 3 of the notes are shared.

### What is an easy Bdim7 for small hands?

The guide tones, ♭3 and ♭♭7 voicing, D4 A♭4, spans 6 semitones or about 83 mm.

### What are the frequencies of Bdim7?

From B3 at A440 in 12-TET: 246.94, 293.66, 349.23, 415.30 Hz.

### What is the set class of Bdim7?

Prime form (0369), Forte 4-28, interval vector &lt;004002&gt;.

### How do I transpose Bdim7 to another key?

Keep the 1, ♭3, ♭5, ♭♭7 formula on the new root. C♯dim7 is C♯, E, G, B♭; Ddim7 is D, F, A♭, C♭.

### Is C♭dim7 the same as Bdim7?

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-7th:b
Last reviewed: 2026-08-12