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

C♯m7♭5 contains C♯, E, G and B. A diminished triad with the minor seventh added on top. C♯ is a black key; E, G and B are white.

- Canonical page: https://piano.org/chords/half-diminished/c-sharp/
- Entity: chord:half-diminished-7th:c-sharp
- Notes: C♯ E G B
- Formula: 1 ♭3 ♭5 ♭7
- Intervals from root: P1, m3, TT, m7
- Interval stack (semitones): 3 3 4
- Also written: C♯m7♭5, C#m7b5, C♯ half diminished 7th
- Parameters: A440, 12-TET, 165 mm octave, spans centre to centre

## Construction

| Degree | Note | Interval from root | Semitones |
| --- | --- | --- | --- |
| 1 | C♯ | Perfect unison | 0 |
| ♭3 | E | Minor third | 3 |
| ♭5 | G | Tritone | 6 |
| ♭7 | B | Minor seventh | 10 |

## Fingering

Rest your right hand over the notes with finger 2 on C♯, finger 3 on E, finger 4 on G, finger 5 on B. 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 | C♯ | C♯3 E3 G3 B3 | 7 | 10 st, 138 mm |
| First inversion (C♯m7♭5/E) | E | E3 G3 B3 C♯4 | 6/5 | 9 st, 124 mm |
| Second inversion (C♯m7♭5/G) | G | G3 B3 C♯4 E4 | 4/3 | 9 st, 124 mm |
| Third inversion (C♯m7♭5/B) | B | B3 C♯4 E4 G4 | 4/2 | 8 st, 110 mm |

## Voicings (10)

| Voicing | Notes | Span | Relation | Omits or adds |
| --- | --- | --- | --- | --- |
| Close, root position | C♯3 E3 G3 B3 | 10 st, 138 mm | identical | none |
| Close, first inversion | E3 G3 B3 C♯4 | 9 st, 124 mm | identical | none |
| Close, second inversion | G3 B3 C♯4 E4 | 9 st, 124 mm | identical | none |
| Close, third inversion | B3 C♯4 E4 G4 | 8 st, 110 mm | identical | none |
| Drop 2 | G2 C♯3 E3 B3 | 16 st, 220 mm | identical | none |
| Drop 3 | E2 C♯3 G3 B3 | 19 st, 261 mm | identical | none |
| Drop 2 and 4 | C♯2 G2 E3 B3 | 22 st, 303 mm | identical | none |
| Shell, root ♭7 ♭3 | C♯2 B2 E3 | 15 st, 206 mm | subset | omits G |
| Guide tones, ♭3 and ♭7 | E3 B3 | 7 st, 96 mm | subset | omits C♯ and G |
| Rootless close | E3 G3 B3 | 7 st, 96 mm | subset | omits C♯ |

## Diatonic function by key

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

Classification system: common-practice functional harmony.

## Progressions (2)

| Progression | Key | Role | Sequence | Voice leading |
| --- | --- | --- | --- | --- |
| vii, I | D major | viim7♭5 | C♯m7♭5 to Dmaj7 | C♯m7♭5 opens the phrase |
| ii, v, i | B minor | iim7♭5 | C♯m7♭5 to F♯m7 to Bm7 | C♯m7♭5 opens the phrase |

## One-edit neighbors

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

## Set theory

- Absolute pitch classes: {1, 4, 7, 11}
- Relative pitch classes: [0, 3, 6, 10]
- Normal order: [11, 1, 4, 7]
- Prime form: (0258)
- Forte number: 4-27
- Interval vector: <012111>

## Frequencies (close root position)

| Note | MIDI | Frequency |
| --- | --- | --- |
| C♯3 | 49 | 138.59 Hz |
| E3 | 52 | 164.81 Hz |
| G3 | 55 | 196.00 Hz |
| B3 | 59 | 246.94 Hz |

## Questions and answers

### What notes are in C♯m7♭5?

C♯m7♭5 contains C♯, E, G and B. The formula is 1, ♭3, ♭5, ♭7.

### How do you play C♯m7♭5 on piano?

Play C♯, E, G and B together. Right hand fingers 2, 3, 4, 5; left hand 5, 4, 3, 2. C♯ is a black key; E, G and B are white.

### What are the inversions of C♯m7♭5?

4 positions: root position C♯ E G B, C♯m7♭5/E, C♯m7♭5/G, C♯m7♭5/B.

### What keys contain C♯m7♭5?

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

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

Drops B. 3 of the notes are shared.

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

The guide tones, ♭3 and ♭7 voicing, E3 B3, spans 7 semitones or about 96 mm.

### What are the frequencies of C♯m7♭5?

From C♯3 at A440 in 12-TET: 138.59, 164.81, 196.00, 246.94 Hz.

### What is the set class of C♯m7♭5?

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

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

Keep the 1, ♭3, ♭5, ♭7 formula on the new root. Cm7♭5 is C, E♭, G♭, B♭; Dm7♭5 is D, F, A♭, C.

### Is D♭m7♭5 the same as C♯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:c-sharp
Last reviewed: 2026-08-12