Measure the narrowest part of your waist and the widest part of your hips and buttocks.

Brand Size Waist (inch) Hip (inch)
S 22.5 - 27.5 29.0 - 33.5
M 23.5 - 29.0 30.5 - 36.0
L 25.0 - 30.5 32.5 - 38.5
XL 26.5 - 32.5 35.0 - 41.0
XXL 28.0 - 34.5 37.0 - 44.0

Natural silk has little stretch. Size up for the best fit.