The bust is measured from underarm seam to underarm seam across the front. Double to get the circumference. The length is measured from the shoulder seam straight down to the hem in the front and back.  
Small: Bust is 22" (44" around), Front length is 30", back length is 34" 
Medium: Bust is 23" (46" around),Front length is 30", back length is 34.5"
Large: Bust is 24" (48" around),Front length is 30.5", back length is 35"
X-Large: Bust is 24.75" (49.5" around), Front length is 31", back length is 35"