The waist is measured from side seam to side seam across the front of the waistband.  Double to get the circumference.  It is then measured across the waist band when stretched out ( double to get the circumference).  The hips are measured across the front at the pockets from side seam to side seam (double to get the circumference).  The length is measured from the waistband straight down to the hem.  The inseam is  measured from the crotch seam straight down to the hem.  
Small: Waist is 13.5" (27" around) but will stretch to 19" (38" around), hips are 22 ", length is 34", inseam is 24"
Medium: Waist is 15" (30" around) but will stretch to 21.5"  (43" around), hips are 24", length is 35", inseam is 24.5"
XL: Waist is 17" (34" around) but will stretch to 23" (46" around), hips are 25.5", length is 37.5",inseam is 27