Sizing:
X-Small: Abdomen Under 30"
              Glutes Under 36"
Small:    Abdomen 30-32" 
              Glutes 37-39"
Medium: Abdomen 33-35"
              Glutes 40-42"
Large:    Abdomen 36-39"
              Glutes 43-45"
If you are in between sizes... go by the glute measurement as the waist is elastic and stretches to cover a wide range.