Root position
A# – C# – EThe root A# is the lowest note. This is the shape most people learn first.
3 notes · 1 · ♭3 · ♭5
A# Diminished Piano Chord (A#dim)
A#dim is built from A#, C# and E — the formula 1 · ♭3 · ♭5, or 3 and 6 semitones above A#. The shape uses 1 white and 2 black keys, and you can hear it, invert it and compare it below.
Chord
A# Diminished
Notes
A# · C# · EFormula
1 · ♭3 · ♭5Right hand
1 · 3 · 5C
D
E
F
G
A
B
C
C#
D#
F#
G#
A#
Choose a chord, then play it. Finger numbers run from thumb (1) to little finger (5).
The finder above already holds A#dim. Press P or the Play chord button to hear A#, C#, E sounded together, then change the root or the chord type to compare it with something else.
Chord tones
The notes in A#dim
A diminished triad is two minor thirds stacked on top of each other, which squeezes the fifth a semitone flat. The result is tense and unresolved. It appears on the seventh degree of a major scale and on the second degree of a minor key, and it usually leads straight back to a more stable chord.
| Note | Interval | Degree | Semitones | Right hand |
|---|---|---|---|---|
| A#black key | Root | 1 | 0 | 1 · thumb |
| C#black key | Minor third | ♭3 | 3 | 3 · middle finger |
| Ewhite key | Diminished fifth | ♭5 | 6 | 5 · little finger |
Step by step
How to play A#dim on piano
- Find A#: it is the third black key in a group of three.
- Build upwards from A# using 3 and 6 semitones to reach C# and E.
- With the right hand, place finger 1 on A#, finger 3 on C# and finger 5 on E. Keep the wrist level and the knuckles rounded.
- Move your hand a little further in towards the fallboard so the black keys sit comfortably under your fingers.
- Play the notes together, then one at a time from the bottom up, and listen to how A#dim settles.
- Try first inversion as well: C# – E – A#. Inversions let you change chords without jumping around the keyboard.
Inversions
A#dim in 3 positions
An inversion keeps the same 3 notes and simply moves the lowest one up an octave. Learning them means you can change chords with small hand movements instead of jumping to a new part of the keyboard.
First inversion
C# – E – A#C# is the lowest note, so the minor third sits in the bass and the notes below it move up an octave.
Second inversion
E – A# – C#E is the lowest note, so the diminished fifth sits in the bass and the notes below it move up an octave.
In context
Which keys contain A#dim
In B major the chord functions as vii°. Altogether it is produced by the scales of 3 keys, so learning it once pays off in several places.
- B majorvii°
- G♯ minorii°
- B harmonic minorvii°
Chord tones are spelled by the degree they occupy, so the third of a minor chord is written as a flat rather than a sharp even though it is the same key on the piano. A double sharp such as F## means the key one whole tone above F.
Compare
A#dim against A# minor
A#dim and A# minor share A# and C#. Moving the perfect fifth E# down 1 semitone to the diminished fifth E turns A# minor into A#dim.
Practise the pair together: hold the shared notes A#, C# still and move only the one finger. Hearing that single change is the quickest way to recognise the two chords by ear.
Open A# minor →Good questions
A#dim questions
What notes are in the A#dim chord?
A#dim contains A#, C# and E. Counted from the root, that is the formula 1 · ♭3 · ♭5, or 3 and 6 semitones above A#.
What is the right-hand fingering for A#dim?
A comfortable beginner fingering is 1 (thumb) on A#, 3 (middle finger) on C# and 5 (little finger) on E. Finger numbers run from the thumb (1) to the little finger (5), and they change once you start using inversions.
How is A#dim different from A# minor?
A#dim and A# minor share A# and C#. Moving the perfect fifth E# down 1 semitone to the diminished fifth E turns A# minor into A#dim.
Which keys use the A#dim chord?
It occurs naturally in B major (vii°), G♯ minor (ii°) and B harmonic minor (vii°). The roman numeral shows which degree of the key the chord is built on.
What are the inversions of A#dim?
root position is A# – C# – E, first inversion is C# – E – A# and second inversion is E – A# – C#. Every inversion holds the same notes; only the lowest one changes.
Is A#dim the same as the B♭ chord?
On an equal-tempered piano A# and B♭ are the same key, so the chords sound identical. Written music chooses between them according to the key signature: pages here are named after the sharp spelling of the root, and the chord tones are then spelled by the degree each one occupies, which is why a double sharp occasionally appears.