The waist is measured from side seam to side seam across the front.  Double to get the circumference.  It is then measured across the waist with the band stretched.  Double to get the circumference.  The hips are measured from side seam to side seam across the front at the hip.  Double to get the circumference.  The length is measured from the waistband to the hem.  The inseam is measured from the crotch seam to the hem. 
 
X-Small: Waist is 10.5" (21" around), Stretch to 22" (44" around); Hips are 21" (442" around); Length is 30"; Inseam is 22"
Small: Waist is 11.5 (23" around), Stretch to 22.5" (45" around); Hips are 23" (46" around); Length is 30.5"; Inseam is 22
Medium: Waist is 13" (26" around), Stretch to 24" (48" around); Hips are 24" (48" around); Length is 31.5"; Inseam is 23"
Large: Waist is 13.5" (27" around), Stretch to 25" (50" around); Hips are 24.5" (49" around); Length is 33"; Inseam is 23.5