---
title: Chord Extensions Explained: Ninths, Elevenths and Thirteenths
dek: Ninths, elevenths and thirteenths are chord tones stacked above the seventh. Which of them fit a chord depends on its quality, and some clash with the third.
topic: jazz
tags: [chord extensions, jazz harmony, ninth chords]
date: 2026-10-11
author: Yunus Emre Vurgun
level: intermediate
related: [chord-symbols-explained, seventh-chords-and-resolution, jazz-chord-voicings-shell-and-rootless, chord-scale-theory]
faq:
  - q: What is a ninth chord?
    a: A ninth chord is a seventh chord with the ninth added, which is the second an octave above the root. In C9 the notes are C, E, G, B flat and D. The chord symbol names the ninth, and the seventh is included with it.
  - q: Why can a major chord not take a natural eleventh?
    a: The natural eleventh is the fourth above the root, F in C. It sits a half step above the major third, E, so the two notes clash. Major chords take a sharp eleventh instead, F sharp in C, which is a whole step from E.
  - q: Do you play every note of a thirteenth chord?
    a: No. A thirteenth chord contains the seventh, ninth and thirteenth, and the eleventh is usually left out because it clashes with the third. A voicing also often drops the fifth, which can go without changing the chord's quality.
  - q: How do you spell a sharp ninth or flat ninth in C?
    a: The sharp ninth of C is D sharp and the flat ninth is D flat. Each chord letter is used once, so the sharp ninth is written as D sharp rather than as E flat, which would repeat the letter E already used for the third.
---

Extensions are the chord tones that continue the stack of thirds past the seventh. In C they are D (the ninth), F (the eleventh) and A (the thirteenth). The chord symbol names the highest extension, and the notes below it are implied: C13 includes the seventh and the ninth, and by convention the eleventh is usually left out. The [chord symbols article](/articles/chord-symbols-explained/) explains how the symbols are read. Each extension changes the colour of the chord, and not every extension fits every chord quality.

## Extensions continue the stack of thirds

A tertian chord is built by stacking thirds: C, E, G, B, D, F, A. The first four notes make a seventh chord. Each note after the seventh is a third above the one before it, B to D, D to F and F to A, so the stack continues in the same letter sequence. Each extension is the same note as a simple interval above the root, one octave higher.

| Extension | Degree | Note in C | Interval above the root |
| --- | --- | --- | --- |
| Ninth | 9 (2nd) | D | major second, an octave up |
| Eleventh | 11 (4th) | F | perfect fourth, an octave up |
| Thirteenth | 13 (6th) | A | major sixth, an octave up |

The extensions are named after the scale degree they take. The ninth is the second, the eleventh is the fourth and the thirteenth is the sixth. A chord can use one of them with or without the note below it, and the symbol tells you which the composer or arranger wants.

## Which extensions each quality takes

A major seventh chord, whose basic form the [seventh chords article](/articles/seventh-chords-and-resolution/) describes, takes the ninth and the thirteenth naturally, and it takes a sharp eleventh well. The natural eleventh, F in C, is a half step above the major third, E. In a major chord the two notes sound against each other, so Cmaj9 with an F natural is usually written as Cmaj9#11, with F sharp instead. The sharp eleventh is a whole step from E and does not clash in the same way.

[keys]E3+B3+D4+F#4[/keys]

That example is Cmaj9#11 with the root omitted: E, B, D and F sharp. The F sharp sounds open where a natural F would sit a half step above the E.

A minor seventh chord takes the ninth naturally, and the eleventh too, but the eleventh is a half step above the minor third, so it is usually voiced without the third. Cm11 is C, E flat, G, B flat, D and F, and in a voicing the E flat is often omitted so that the F has room. The thirteenth, A, is the natural sixth above C, which is the raised sixth of the Dorian mode. Adding it gives a minor chord a Dorian sound rather than a plain minor one.

A dominant seventh takes the most extensions, both natural and altered. The natural ninth and thirteenth fit C9 and C13. The altered extensions are the flat ninth, the sharp ninth, the sharp eleventh and the flat thirteenth. These are the notes that make a dominant chord sound tense, and they are the reason scales such as the altered scale and the lydian dominant are paired with dominant chords (see the [chord-scale article](/articles/chord-scale-theory/)).

The natural extensions of a plain dominant are the easiest to hear, because they come from the scale the chord already uses. Over G7 the ninth is A and the thirteenth is E. Both belong to G Mixolydian, which is G, A, B, C, D, E, F, so a G13 with the ninth and thirteenth added is built entirely from the notes of that scale. The eleventh, C, is the one note of Mixolydian that clashes, and that is why it is the one left out.

## Altered extensions and the spelling rule

Altered extensions are written with a flat or sharp sign on the scale degree. In C, the flat ninth is D flat, the sharp ninth is D sharp, the sharp eleventh is F sharp and the flat thirteenth is A flat. The usual spelling rule is that each letter appears only once in a chord. The sharp ninth is D sharp because the ninth is the letter D. Writing it as E flat would repeat the letter E already used for the third, and the chord would be misspelled even though it sounds the same on the keyboard.

[keys]E3+Bb3+D4 E3+Bb3+D#4[/keys]

The first chord is C9 without its root: E, B flat and D. The second is C7 with a sharp ninth: E, B flat and D sharp. Only one note changes, and the half step between D and D sharp is the whole difference. The sharp ninth also sits a half step below the third, E, and that clash is what gives the chord its edge.

## Voicing economy: three or four notes per chord

Extensions add notes, so a voicing usually removes others. The fifth is the first to go, because it rarely changes the chord's quality. The root is the next, when a bass player is covering it. What remains is the third, the seventh and one or two extensions, and those notes carry the chord.

The four chords below are C9, Cmaj9, Cm9 and C13, each voiced as third, seventh and ninth, with the thirteenth added to the last. The first and second chords differ only in the seventh, B flat in C9 and B natural in Cmaj9. The third differs from the first only in the third, E flat rather than E.

[keys]E3+Bb3+D4 E3+B3+D4 Eb3+Bb3+D4 E3+Bb3+D4+A4[/keys]

The C13 in the last chord omits the eleventh, F, and keeps the thirteenth, A, and the ninth, D. That is the usual reduction. A full thirteenth chord would contain all seven of its tones, and no one plays all of them at once.

Keep the extensions above the third and seventh, as the examples in the [shell and rootless voicings article](/articles/jazz-chord-voicings-shell-and-rootless/) do. When a ninth is placed in the bass, it competes with the root and the third for the listener's attention, and the chord's quality becomes harder to hear. The extensions are colour, and colour is easiest to hear on top of a clear harmony.

The table below gives the spelled notes for the chord symbols most often seen in lead sheets. The eleventh in the minor chord is listed in full, although a voicing would drop the third.

| Symbol | Extensions | Full spelling in C |
| --- | --- | --- |
| Cmaj9 | 9 (D) | C E G B D |
| Cmaj9#11 | 9 (D), #11 (F#) | C E G B D F# |
| Cm9 | 9 (D) | C Eb G Bb D |
| Cm11 | 9 (D), 11 (F) | C Eb G Bb D F |
| C9 | 9 (D) | C E G Bb D |
| C7b9 | b9 (Db) | C E G Bb Db |
| C7#9 | #9 (D#) | C E G Bb D# |
| C7#11 | #11 (F#) | C E G Bb F# |
| C13 | 9 (D), 13 (A), 11 omitted | C E G Bb D A |
| C7b13 | b13 (Ab) | C E G Bb Ab |

## Where this misleads people

The first error is to read a symbol as a full spelling. C13 names a chord with seven notes, and a player who tries to voice all seven will produce a thick, muddy sound. The symbol tells you the highest note the chord may use, and the voicing decides what is actually played.

The second error is adding the natural eleventh to a major chord because it is in the stack. The note is correct arithmetic and wrong sound. Use the sharp eleventh, or leave the eleventh out.

The third error is to treat every alteration as an equal colour. A sharp ninth on a dominant chord is a choice that depends on the scale and on where the chord is going, not a default that can be added anywhere. The same note over a chord with a different quality can clash in a different way.

## What to do with it

Play the four-chord example in the voicings section, C9, Cmaj9, Cm9 and C13, and listen to how one note changes the quality each time. Then take C9 and move only the ninth up and down by a half step: D flat, D, and D sharp. Listen for which one sounds like a colour and which one sounds like a mistake, and why. Finally, repeat the same third, seventh and ninth pattern in another key by moving every note by the same interval, and check the spelling of each chord letter by letter.