If you don't already have a couple of these, what are you doing? You absolutely need at least a few.
Pieces run true to size unless stated otherwise in "Details" tab to the left.
Bust
XS/S - 32-34 A-B
M - 34-36 C
L - 36+ C-D
Waist
S - 24-25
M - 26-27
L - 28-29