Chord Extensions for Jazz Piano (How to Use 9ths, 11ths & 13ths)
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If your chords sound basic, you’re probably stopping at 7ths.
Chord extensions are what you’re missing.
This is one of the biggest upgrades you can make to your jazz piano playing.
Most beginners learn 7th chords… and stop there.
But real jazz sound comes from going further—adding the 9ths, 11ths, and 13ths that give chords their color and depth.
The problem is, chord extensions often feel confusing:
Where do these numbers come from?
Why does a C7 use notes from a major scale?
What do symbols like b9, #11, or 13 actually mean?
In this lesson, you’ll clear all of that up—and learn a simple system to find and use chord extensions in any key.
And if you want to see how chord extensions fit into the bigger picture of jazz piano—chords, progressions, improvisation, and how everything connects—start here:
👉 Learn Jazz Piano from the Ground Up →
Then come back to this lesson and apply these extensions with real understanding.
What are Chord Extensions?
In jazz, ‘chord extensions’ are the 9th, 11th, and 13th of a chord. So jazz chords are built in 3rds, and when you play up the scale in 3rds (every other note) it takes you all the way up to the 13th.
The lower four notes (1 3 5 7) are known as 'chordal tones', and the upper three notes (9 11 13) are known as 'chord extensions', or simply 'extensions':
How to Find a Chord Extension
Chord extensions cause a lot of confusion to students because you would think they’d be different, depending on what type of chord it is - you'd think that major chords would have major extensions, minor chords would have minor extensions, and so on.
However, it's much simpler than that:
Chord extensions are always built from the major scale - regardless of what type of chord it is - that goes for minor 7 chords, V7 chords, minor-major 7 chords, and so on.
So to find the 9th, b, or b of a chord - just imagine a major scale running up from the chord’s root.
So for a C7 chord, you’d walk up the notes of C major scale to find each extended note:
- The 2nd of the scale is also the 9th = D.
- The 4th of the scale is also the 11th = F.
- The 6th of the scale is also the 13th = A.
Altered Chord Extensions
But what if the chord symbol contains an altered chord extension (sharpened or flatenned) - like 'C7b9', or 'C7#11', or 'C7b13'?
Not a problem - just find the natural chord extension first (by running up the major scale), and then flatten it or sharpen it:
Some Examples
So let's say I saw the chord symbol 'C7b9' - first I would find the natural 9th by running up C major scale to the 2nd (9th) - which would be D:
Next, I would flatten the 9th by lowering it one half-step - to Db:
Or let's say the chord symbol was 'C7#9' instead - in this case you would sharpen the 9th, so D would become D# (or Eb):
This is the exact process you would go through to add any chord extension (11th, #11th, 13th, b13th) to any chord (C min 7, C maj 7, etc).
Alternative Numbers Used in Jazz
Another source of confusion is the different numbers you'll sometimes see used in chord symbols - sometimes you'll see '13', whereas other times you'll see '6'. Or simetimes you'll see '11' whereas other times you'll see '4'.
Most of the time, chord extensions are written using odd numbers - ‘9’, '11’ and ’13’ - this way it reinforces the fact that chords are stacks of 3rds (1 3 5 7 9 11 13).
However, there are a couple of numbering conventions which have 'caught on' - when it comes to the use of '13' vs '6', and '11' vs '4':
'6' or '13'?
Over a C chord, the numbers ‘6’ and ’13’ both refer to the same note, A. However, if the chord is a major or minor chord, then the arranger will use the number ‘6’: 'C6' or 'Cm6'.
Whereas if the chord is a V7 chord, then the arranger will use ‘13’, 'C13':
Note that in the C13 chord, the 7th is being played below the 13th. Whereas in the C6 and Cm6 chords there is no 7th - the 6th is played instead of the 7th.
'4' or '11'?
Simarly, over a C chord, the numbers ‘4’ and '11’ both refer to the same note, F.
However, if the chord is a minor 7 chord or a V7 chord, then it’s common to use the number '11’ (this will usually be a #11 over V7 chords).
Whereas if the chord is a major 7 chord, then most arrangers will write ‘4’ (e.g. 'C maj 7 #4'):
Note that not all real books follow this 4/11 numbering convention - sometimes you’ll see ‘C maj 7 #11’ in a lead sheet - so just remember that both numbers (4 and 11) mean the same note, they’re just numbered differently based on the type of chord it is.
Sus 4 Chords Explained
One final chord to cover is the ‘sus 4 chord’ - short for ‘suspended 4th’. In jazz, a sus 4 means to play the chord’s 4th instead of the 3rd.
Here’s how ‘C7 sus 4’ looks - notice how I'm playing the chord's 4th (F) instead of the 3rd (E):
NOTE: In other styles of music (like classical music), a ‘suspended 4th’ would normally resolve to the chord’s 3rd, before changing to the next chord. However in jazz, the sus 4 is held for the full duration of the chord.
Sus 4s are most commonly applied to V7 chords. Here are a couple of my favorite chord voicings for C7 sus 4:
First, you can simply play a Bb major triad over C - this chord voicing can be heard famously in 'Song For My Father' by Horace Silver:
Or you can play a Bb major 7 chord in your right hand, over C in the bass:
All Jazz Chords – Review
Here's my 3-minute run through of all common Jazz chords – from 7ths, 9ths, 11ths, 13ths, altered, and more:
Summary
Well done, you made it! In this jazz piano lesson we covered:
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How chord extensions work - 9ths, 11ths and 13ths are always built from the chord's major scale, even when it's a minor chord!
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How to find altered chord extensions - find the natural chord extension first (from the major scale), then sharpen or flatten it.
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Why different numbers are sometimes used - '6' is used for major and minor chords, '13' for V7 chords. '11' is used for minor 7 and V7 chords, '4' for major 7 chords.
Next step
If you’d like the full written version of my Ultimate Jazz Piano Guide — an encyclopedia-style lesson covering Jazz piano theory, chords, voicings, scales, improvisation and harmony — explore it here:
Or focus on one area:
Jazz Piano Fundamentals →
Chord Voicings →
Improvisation →
I’m Julian Bradley, founder of Jazz Tutorial.
What you get here is one clear teaching philosophy — not a mix of conflicting approaches.
Simple. Structured. No confusion.