Chord · A Dominant 9th
A9 Chord
A9 is A, C#, E, G and B — funky, soulful; James Brown territory.
A9 on every instrument
The same 5 notes, 4 sets of hands. Open a diagram for alternate shapes, audio and the mistakes to avoid.
What A9 is made of
A9 (A ninth) is built from the notes A, C#, E, G, B, with the interval pattern 1, 3, 5, b7, 9.
Stack 1, 3, 5, b7 and 9 on a root of A and you get A, C#, E, G and B. That interval recipe is what makes the chord a ninth chord — move the same shape to another root and the character travels with it, which is why C9 sounds like a transposed A9.
Dominant 9th: Funky, soulful; James Brown territory.
Spelling: the notes above are written the way a score would write them, not simplified to the nearest piano key. That is why this chord is spelled with C♯ rather than its enharmonic equivalent.
Keys that contain A9
All 5 notes sit inside the scale of 2 keys. The roman numeral marks the degree the chord is rooted on.
Major keys
Minor keys
Other chords on A
Same root, different colour.
The same ninth shape, moved
The identical interval recipe, built on other roots.
Questions people ask about A9
- What notes are in the A9 chord?
- A9 is made of A, C#, E, G and B — the 1, 3, 5, b7 and 9 degrees of a ninth chord built on A.
- What keys use the A9 chord?
- Every note of A9 belongs to 2 keys: D Major (V), B Minor (VII). The roman numeral is the scale degree the chord is rooted on.
- How do you play A9 on guitar and piano?
- This page shows A9 on guitar, piano, ukulele and mandolin — 8 voicings in total. Each diagram links to the full instrument page with alternate shapes, audio and common mistakes.
Learn the theory behind it
Why A9 behaves the way it does — the guides that explain the chord instead of just spelling it.