Fdim is a diminished, spelled F, Ab and Cb. In Standard tuning (E2 A2 D3 G3 B3 E4) the easiest shape is xx3404, which sits at fret 3, spans 1 fret, lets 1 string ring open and mutes 2 strings. 12 positions for it are shown below, from the nut up to fret 13.
Notes and intervals
Note
F
Ab
Cb
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.
xx3404sits at fret 3, spans 1 fret, lets 1 string ring open and mutes 2 strings12310xsits at fret 1, needs a barre across 4 strings at fret 1, lets 1 string ring open and mutes 1 stringx23404sits at fret 2, spans 2 frets, lets 1 string ring open and mutes 1 stringx89109xsits at fret 8, spans 2 frets and mutes 2 stringsxx6464sits at fret 4, needs a barre across 3 strings at fret 4 and mutes 2 strings131415130xsits at fret 13, needs a barre across 4 strings at fret 13, lets 1 string ring open and mutes 1 string786xxxsits at fret 6, spans 2 frets and mutes 3 stringsxxx1097sits at fret 7, spans 3 frets and mutes 3 stringsx119100xsits at fret 9, spans 2 frets, lets 1 string ring open and mutes 2 stringsxxx131213sits at fret 12, spans 1 fret and mutes 3 strings131115130xsits at fret 11, spans 4 frets, lets 1 string ring open and mutes 1 stringxx310xsits at fret 1, spans 2 frets, lets 1 string ring open and mutes 3 strings
Keys Fdim belongs to
Fdim is diatonic to 8 of the 96 keys this app knows, playing a different role in each.