A dominant 7th sharp 9 chord

Playing it

There’s no open-string way to play A7♯9 on guitar with the root in the bass, so the standard shape is a barre across the 5th fret (575658).

On piano, A7♯9 has one black key (C♯) and four white keys. In root position it spans more than an octave, so many pianists play the root with the left hand and the rest with the right.

On ukulele it takes a single finger (0004), which makes A7♯9 one of the simplest chords on the instrument. It leaves out the root, which a bass player (or your ear) fills in.

Related chords

Move a single note and A7♯9 becomes a different chord: drop the B♯ for A7, drop the C♯ for Am7, lower B♯ to B for A9 and swap C♯ for B for Am9.

Where you’ll hear it

Notice the B♯ in A7♯9 (A C♯ E G B♯): each note of the chord takes its own letter (A–C–E–G–B), so the augmented 9th has to be written B♯ rather than C — the same key on a piano, spelled to fit the chord.