C#sus4 is C#, F# and G# — C# with the third replaced by the fourth.
It sounds suspended mid-air. Played before the plain chord it is the oldest tension-and-release move there is.

| C# | F# | G# |
|---|---|---|
| 1 | 4 | 5 |
Suspended — classically it resolves down onto the third.
Also written C#sus or C# suspended 4th. The same chord either way; which spelling you meet depends on who wrote the chart.
C#sus4 in 2nd inversion puts G# in the bass instead of C#, the 5th of the chord. The notes are the same; what changes is what the bass line does, which is most of why you would reach for it — it lets the lowest voice move by step where the root would have jumped.
One of C#sus4’s 6 common shapes does this: xx6679.
Start with x4412x — no barre and down at the nut. None of the shapes for C#sus4 uses an open string, so every one of them is movable; the lowest sits at the 1st fret. 1 of the 6 needs a barre. Together they cover the neck from the 1st fret to the 14th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x4412x | 1st fret | C#, root position | C# | all fretted |
| x46674 | 4th fret | C#, root position | G# | all fretted |
| 9x6679 | 6th fret | C#, root position | C# | all fretted |
| xx6679 | 6th fret | G#, 2nd inversion | C# | all fretted |
| 9-11-11-11-9-9 | 9th fret | C#, root position | C# | barred |
| x-x-11-13-14-14 | 11th fret | C#, root position | F# | all fretted |
The same notes rebuilt from scratch give 46 triad voicings, each on its own page.
Voice by voice, C#sus4 → C#. One voice moves by a semitone, and 2 notes are common to both chords.
| In C#sus4 | Moves | In C# |
|---|---|---|
| C#, the root | stays where it is | C#, the root |
| F#, the fourth | falls a semitone | E#, the major third |
| G#, the fifth | stays where it is | G#, the fifth |
In which keys. Every note of C#sus4 belongs to C# major (the I), C# minor (the i), Eb minor (the ♭VII), E major (the vi), F# major (the V), F# minor (the v), Ab minor (the iv), A major (the iii), Bb minor (the ♭III) and B major (the ii).
Every note of C#sus4 is in C# minor pentatonic, C# blues, C# major, C# mixolydian and C# dorian.
Change one note of C#sus4 and you have C# (the fourth becomes a major third), C#m (the fourth becomes a minor third), C#sus2 (the fourth becomes a ninth), C#sus2sus4 (add the ninth), C#5 (drop the fourth) or C#7sus4 (add the flat seventh).
C#sus4 is a suspended chord — root and fifth, with a second or fourth where the third would be — or nothing at all. Suspended and power chords on every root.
On C#sus4’s sound and use this page follows Edward Aldwell & Carl Schachter, Harmony and Voice Leading (Schirmer / Cengage, 4th ed., 2011). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.