Bdim is a diminished, spelled B, D and F. In Open G tuning (D2 G2 D3 G3 B3 D4) the easiest shape is x40403, which sits at fret 3, 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 10.
Notes and intervals
Note
B
D
F
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.
x40403sits at fret 3, spans 1 fret, lets 2 strings ring open and mutes 1 string91001000sits at fret 9, spans 1 fret and lets 3 strings ring openx40400sits at fret 4, needs no stretch at all, lets 3 strings ring open and mutes 1 string970760sits at fret 6, spans 3 frets and lets 2 strings ring open9701000sits at fret 7, spans 3 frets and lets 3 strings ring open01001000sits at fret 10, needs no stretch at all and lets 4 strings ring openx43400sits at fret 3, spans 1 fret, lets 2 strings ring open and mutes 1 stringx40433sits at fret 3, needs a barre across 2 strings at fret 3, lets 1 string ring open and mutes 1 stringx43430sits at fret 3, needs a barre across 3 strings at fret 3, lets 1 string ring open and mutes 1 stringx43433sits at fret 3, needs a barre across 4 strings at fret 3 and mutes 1 stringx40430sits at fret 3, spans 1 fret, lets 2 strings ring open and mutes 1 string040403sits at fret 3, spans 1 fret and lets 3 strings ring open
Keys Bdim belongs to
Bdim is diatonic to 8 of the 96 keys this app knows, playing a different role in each.