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 and also to the side slit.
XS: Bust is 24" (48" around), length to side slit is 32, center length is 39"
S/M: Bust is 25' (50" around), length to side slit is 33, center length is 39.5"
L/XL: bust is 26" (52" around), length to side slit is 33, center length is 39.5"