Bdim piano chord, B diminished notes and fingering.

The Bdim piano chord is B diminished: the notes B, D and F. It is two minor thirds stacked on top of each other. B up to D is three semitones, and D up to F is three more, so the fifth (F) is lowered to six semitones above the root. Chord charts write it as Bdim or B°.

How to play Bdim on piano

1. Find B on the keyboard. B is the white key just right of the group of three black keys, the last white key before C.
2. With your right hand, put finger 1 on B, finger 3 on D and finger 5 on F. Finger 1 is the thumb.
3. Press all three keys together. In root position they run from B3 to F4, a reach of 6 semitones. Play chord sounds them together and Arpeggio sounds them one by one, from the bottom up.
4. Click Left hand to see the left hand. It plays B2 to F3, one octave lower: B with finger 5, D with finger 3, F with finger 1.
5. The cards under the keyboard hold the three positions, with B, D and F at the bottom in turn. Play and Arpeggio on a card play that position.
6. Open Note names. Every note of this chord is a white key, so the Sharps and Flats choices show the same names.

How Bdim is built

Counted from the root, the formula is 0, 3, 6. Stacked on each other the gaps are 3 + 3: two minor thirds. Compare it with B minor (B, D and F#): the first two notes are the same, and the fifth is lowered one semitone from F# to F. A perfect fifth is seven semitones; this one is six, and six semitones is a tritone.

Worked example: the pitch of B3. On a piano tuned to A4 = 440 Hz, a note 10 semitones below A4 has the frequency 440 × 2^(-10/12), which is about 246.94 Hz. D4 is 7 semitones below A4, so 440 × 2^(-7/12) gives about 293.66 Hz.

What the keys look like under your hand

B has a black key on its left (Bb) and none on its right, because B and C are only a semitone apart. All three notes are white keys (B, D and F), so the hand can stay flat and there is no reaching for a black key. The thumb (B) and little finger (F) are both on white keys here, so the hand can lie in its natural shape.

Bdim inversions and fingering

Bdim has three positions. In root position B is at the bottom. In the first inversion, D is at the bottom and the chord is written Bdim/D. In the second inversion, F is at the bottom and the chord is written Bdim/F. The tightest reach, 6 semitones from the lowest key to the highest, is the root position. The widest, at 9, is the first inversion and second inversion.

The keys that hold Bdim

Bdim fits two of the major and natural minor keys that have a standard key signature, which means every note of it comes from that key's scale. The simplest is C major, with no sharps or flats, where it is chord vii°.

Progressions that use Bdim, with the chord numbers and the chords in that key:

• C major: IV-vii°-iii-vi, which is F, Bdim, Em, Am, a run of falling fifths.
• A minor: ii°-v-i, which is Bdim, Em, Am, the minor ii-V-i, with the natural minor v.
• C major: vii°-I, which is Bdim, C, the diminished chord leading up to the tonic.

Here is a worked example in C major. The chord before Bdim in the first progression above is F (F, A and C). From F in root position, the closest way to reach Bdim is its second inversion (F, B and D, lowest note first): one note stays where it is, and the others move 4 semitones in total, counting each note against the note in the same place from the bottom.

Bdim also sits inside G7 (G, B, D and F): take the root off that dominant 7th and the notes left over are B, D and F.

What Bdim sounds like

A diminished triad sounds tense and unresolved. It rarely sits still: the usual move is up a semitone to the chord built on C. It is used as a passing chord between two others and as a spice inside a progression.

Bdim is the vii° chord in C major and the ii° chord in A minor. It is also chord vii° of C minor, using the raised seventh of the harmonic minor scale.

A common mistake with Bdim

A common mistake is pressing F# instead of F, one semitone higher than the fifth of Bdim. That gives Bm (B, D and F#), a plain minor chord. The top key of Bdim is a semitone lower than you might expect, so check it against the chord of the same root.

Chords to learn next

Chords close to Bdim: B minor (raises the fifth; shares B and D); G7 (the dominant 7th it sits inside; contains all its notes); C major (the chord it leads to; shares no note); Bm7 (adds a minor seventh to the minor chord; shares B and D).

Once Bdim feels easy, play it and then C major to hear it resolve upward. For chords beyond these six types, and for guitar and ukulele shapes, use the chord finder. To play along with your computer keys, open the virtual piano. The piano chords page lists all 72 chords.