How To Build 9th Chords.

[zarapr]

Lots of good info here.

[MadBrain]

The space between white notes is either a major or minor interval depending on what note you start from:
2nds: major: C-D, D-E, F-G, G-A, A-B; minor: E-F, B-C
3rds: major: C-E, F-A, G-B; minor: D-F, E-G, A-C, B-D
4ths: perfect: C-F, D-G, E-A, G-C, A-D, B-E; augmented: F-B
5ths: perfect: C-G, D-A, E-B, F-C, G-D, A-E; diminished: B-F
6ths: major: C-A, D-B, F-D, G-E; minor: E-C, A-F, B-G
7ths: major: C-B, F-E; minor: D-C, E-D, G-F, A-G, B-A

If the type doesn't match with what you need for your chord (E-F is a minor 2nd, you need a major 2nd in a 9th chord), then you need to add a sharp or a flat.

min2 (1 fret): b9
maj2 (2 frets): 9, add9, sus2
min3/aug2 (3 frets): m, min, -, #9
maj3 (4 frets): (assumed by default, removed by sus2/sus4/11 or m/min/- but not #9)
4 (5 frets): sus4, 11
dim5/aug4 (6 frets): dim, b5, °, #11
5 (7 frets): (assumed by default, removed by dim/b5/° or #5)
aug5 (8 frets): +, aug, #5
maj6/dim7 (9 frets): 6, 13, dim7, °7
min7 (10 frets): 7 (also implied by 9, 11 and 13)
maj7 (11 frets): maj7, Δ (also implied by maj9 and maj13)

So for instance take the chord C7#5#9:
aug2 ("#9"): C-D is a major 2nd, not okay, we need to turn D into D#
maj3 (implied): C-E is already a major 3rd, no change needed
aug5 ("#5"): C-G is a perfect 5th, not okay, we need to turn G into G#
min7 ("7"): C-B is a major 7th, not okay, we need to turn B into Bb

Final chord: C, D#, E, G#, Bb

[ImNotDedYet]

Here's a cheat for finding the 9ths. Think of the 2nd in the scale of the musical key, and that's essentially your 9th. Often you'll play it an octave higher, but not always. 13th - that's your 6th. 11th is your 4th.

MadBrain's post is a good one, but he left out dominant 7ths - which are a major triad (first three notes of the chord is a major chord) with a flat 7th. Very useful to get the ii - V - I.

[Mister Natural]

Here's a cheat for finding the 9ths. Think of the 2nd in the scale of the musical key, and that's essentially your 9th. Often you'll play it an octave higher, but not always. 13th - that's your 6th. 11th is your 4th

. . . I was just gonna say that !

if one accepts any chord in it's inverted shape - the above applies even more obviously