Learn › A9 Chord on Piano (A Dominant 9th)
New Released in April 2026
A9 Chord on Piano (A Dominant 9th)
A9, the A dominant 9th chord, is the dominant seventh A7 plus the 9th, B. Its notes on the piano are A, C#, E, G and B. In one phrase: full and bluesy-bright, tension that still sounds smooth.
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- MIDI keyboard
- Digital or acoustic piano
- Guitar
- Computer, phone or tablet
The formula of A9
Every chord is a recipe of scale steps. For A9 the recipe is 1 3 5 b7 9, counted from A.
Start chord: A7
| Note | Step | Interval | Keys from A |
|---|---|---|---|
| A | 1 | root | 0 |
| C# | 3 | major 3rd | 4 |
| E | 5 | perfect 5th | 7 |
| G | b7 | minor 7th | 10 |
| B | 9 | major 9th | 14 |
A9 in every position
Same notes, different order. Pick the position closest to the chord you just played.
Both hands: A G C# E B
Rootless, 3rd on the bottom: C# E G B
Rootless, 7th on the bottom: G B C# E
Left hand alone: A G
Which fingers
| Left hand | A G | 5 1 |
|---|---|---|
| Right hand | C# E B | 1 2 4 |
A second name for the same keys
Above the root A sit four notes that form C#m7b5: C# E G B. A pianist can play A with the left hand and C#m7b5 with the right, and the result is A9.
When to play A9
- A9 is the V chord of D major: it pulls home to D.
- Many pianists play A9 whenever A7 appears, because the 9th makes the same pull sound richer.
Make A9 automatic
- Say the notes out loud while you press them: A, C#, E, G and B.
- Switch between A7 and A9 ten times without looking at your hand.
- Alternate root position and a rootless shape with the 3rd on the bottom, keeping shared notes still.
- Then test it in random order among other chords: recall under time pressure is what sticks.
Keep each session short and frequent and A9 will become automatic.
Turn A9 into a reflex
In ChordRunner every correct chord moves your runner forward. Plug in a MIDI keyboard or let the microphone listen to your piano. Dominant 9ths appear in the later boss challenges, next to major and minor 9ths.
Play the demoCommon questions
What is A9 on the piano?
A9 is the A dominant 9th chord: A, C#, E, G and B, the dominant seventh A7 plus the 9th, B.
Is A9 the same as C#m7b5?
Not quite: C#m7b5 (C# E G B) is only the upper part of A9. Add A underneath and you have the full A9.
Where is A9 used?
A9 is the V chord of D major: it pulls home to D. Many pianists play A9 whenever A7 appears, because the 9th makes the same pull sound richer.
Can I practise A9 with a MIDI keyboard or a real piano?
Yes. In ChordRunner a USB MIDI keyboard is detected automatically, and an acoustic or digital piano works through the microphone. The game checks that A, C#, E, G and B sound together.
Your instrument is the controller.
ChordRunner is a browser game that teaches piano and guitar chords: a chord appears on screen, you play it on a real instrument, and your runner jumps. MIDI keyboard or microphone, both work.
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