Measure your waist.
XS: 76 cm (30 inches)
S: 82 cm (32 inches)
M: 88 cm (34 inches)
L: 94 cm (37 inches)
XL: 100 cm (39 inches)
XXL: 106 cm (42 inches)
Grab your normal size. Sabbes are the same size as all other top underwear brands (Calvin Klein, Nike, Björn Borg, etc).