Women's size chart - sizes XS to 4XL:

For a good fit you need your body measurements.

Size XS S M L XL XXL 3XL 4XL
Body measurements (in cm)
B Waist circumference 62-66 66-70 70-74 74-78 78-82 83-86 86-90 90-94
C Hip circumference 72-76 76-80 80-84 84-88 88-92 92-106 106-110 110-114
General height basis: 168 cm.

To get the exact body measurements, it is easiest if you have some help from a friend. The measurements are taken directly on the body - in underwear only.