C#dim is a diminished, spelled C#, E and G. In Standard tuning (E2 A2 D3 G3 B3 E4) the easiest shape is x45050, which sits at fret 4, spans 1 fret, lets 2 strings ring open and mutes 1 string. 12 positions for it are shown below, from the nut up to fret 14.
Notes and intervals
Note
C#
E
G
Interval
1P
3m
5d
12 ways to play it
Ordered by how hard they are to fret, easiest first, one per position on the neck. Fret numbers are relative to the position marked beside each grid.
x45050sits at fret 4, spans 1 fret, lets 2 strings ring open and mutes 1 stringx42020sits at fret 2, spans 2 frets, lets 2 strings ring open and mutes 1 stringx45053sits at fret 3, spans 2 frets, lets 1 string ring open and mutes 1 stringxxx650sits at fret 5, spans 1 fret, lets 1 string ring open and mutes 3 stringsxxx680sits at fret 6, spans 2 frets, lets 1 string ring open and mutes 3 strings91011080sits at fret 8, spans 3 frets and lets 2 strings ring open910119xxsits at fret 9, needs a barre across 4 strings at fret 9 and mutes 2 strings010110xxsits at fret 10, spans 1 fret, lets 2 strings ring open and mutes 2 strings9711080sits at fret 7, spans 4 frets and lets 2 strings ring openxx110140sits at fret 11, spans 3 frets, lets 2 strings ring open and mutes 2 stringsxxx0140sits at fret 14, needs no stretch at all, lets 2 strings ring open and mutes 3 stringsxx1401412sits at fret 12, spans 2 frets, lets 1 string ring open and mutes 2 strings
Keys C#dim belongs to
C#dim is diatonic to 8 of the 96 keys this app knows, playing a different role in each.