Bdim7: B Diminished 7th Piano Chord

Root position: either hand, fingers low note to high
Hand	Notes	Fingers
Right	B, D, F, A♭	1-2-3-5
Left	B, D, F, A♭	5-3-2-1

Scale degree, note, and interval measured from the root.
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

Construction

B Diminished 7th = Root + Minor 3rd + Diminished 5th + Major 6th = B, D, F, A♭

Note	Interval	Degree
B	Root	1
D	Minor 3rd	♭3
F	Diminished 5th	♭5
A♭	Major 6th	6

Fingering

Note	Key color	Right hand	Left hand
B	white	thumb (1)	little finger (5)
D	white	index finger (2)	middle finger (3)
F	white	middle finger (3)	index finger (2)
A♭	black	little finger (5)	thumb (1)

Right hand: thumb (1) on B, index finger (2) on D, middle finger (3) on F, little finger (5) on A♭.

Left hand: little finger (5) on B, middle finger (3) on D, index finger (2) on F, thumb (1) on A♭.

B Diminished 7th Inversions

Root position
B – D – F – A♭
1st inversion (Bdim7/D)
D – F – A♭ – B
2nd inversion (Bdim7/F)
F – A♭ – B – D
3rd inversion (Bdim7/A♭)
A♭ – B – D – F

Key Signature

A Diminished 7th chord is built from symmetrical or ambiguous intervals, so it doesn't belong to a single key and has no key signature of its own.

Chords in the Key of B Major

These are the triads built on each degree of B Major:

I — B Major (major)

Degree	Numeral	Chord	Quality
1	I	B Major	Major
2	ii	C♯ Minor	Minor
3	iii	D♯ Minor	Minor
4	IV	E Major	Major
5	V	F♯ Major	Major
6	vi	G♯ Minor	Minor
7	vii°	A♯ Diminished	Diminished

Same Notes, Other Names

The notes B – D – F – A♭ aren’t exclusive to this chord. Depending on which note is the bass and how the chord functions, the same pitches also spell the following:

A♭ Diminished 7th→D Diminished 7th→F Diminished 7th→

B Diminished 7th : Frequently Asked Questions

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 <004002>.

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.

B Diminished 7th in detail

Exact

Every pitch class is present and nothing outside the chord is added.

Type	Notes	Semitones	Span	Omissions and additions	Set relation
Close, root position	B3 D4 F4 A♭4	9	124 mm	none	identical
Close, first inversion	D4 F4 A♭4 B4	9	124 mm	none	identical
Close, second inversion	F4 A♭4 B4 D5	9	124 mm	none	identical
Close, third inversion	A♭4 B4 D5 F5	9	124 mm	none	identical
Drop 2	F3 B3 D4 A♭4	15	206 mm	none	identical
Drop 3	D3 B3 F4 A♭4	18	248 mm	none	identical
Drop 2 and 4	B2 F3 D4 A♭4	21	289 mm	none	identical

Reduced

A subset of the pitch classes: the identity is incomplete rather than altered.

Type	Notes	Semitones	Span	Omissions and additions	Set relation
Shell, root ♭♭7 ♭3	B2 A♭3 D4	15	206 mm	omits F	subset
Guide tones, ♭3 and ♭♭7	D4 A♭4	6	83 mm	omits B and F	subset
Rootless close	D4 F4 A♭4	6	83 mm	omits B	subset

Spans are measured centre to centre at a 165 mm octave (standard keyboard geometry).

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

One position per chord tone in the bass. Spans are for close position: voiced inversions appear under Voicings.

Change one note

Chords a single note away, and what moving that note does.

Chord	Change	Formula	Common tones
Bdim	drops A♭	1 ♭3 ♭5	3
Bm7♭5	A♭ becomes A	1 ♭3 ♭5 ♭7	3
Bm6	F becomes F♯	1 ♭3 5 6	3
Bm	F, A♭ becomes F♯	1 ♭3 5	2
Bm7	F, A♭ becomes F♯, A	1 ♭3 5 ♭7	2
BmMaj7	F, A♭ becomes F♯, A♯	1 ♭3 5 7	2
B6	D, F becomes D♯, F♯	1 3 5 6	2

Frequencies

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

Reference pitch A440, 12-TET, close root position.

Set theory: prime form, Forte number, interval vector

Absolute pitch class set: {11, 2, 5, 8}
Normal order: [2, 5, 8, 11]
Prime form: (0369)
Forte number: 4-28
Interval vector: <004002>

Pair	Interval	Semitones	Interval class
B to D	Minor third	3	3
B to F	Tritone	6	6
B to A♭	Major sixth	9	3
D to F	Minor third	3	3
D to A♭	Tritone	6	6
F to A♭	Minor third	3	3

Where these facts come from

Every value on this page is derived from the note formula for a diminished 7th applied to the root B, using standard music theory. Nothing here is hand-entered per chord, so the notes, intervals, inversions and frequencies cannot drift out of agreement with each other. Pitches assume 12-TET at A440.

B Diminished 7th

Fingerings

B Diminished 7th: notes and degrees