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 to the hem in the center and the hem on the side.  The Kendal Green does run smaller 
New Gray: (available in xs, small)
X-Small: Bust 18.5 (37" around), center length is 25", and side length is 30" (Plain 3/4 length sleeve without the gathering at the elbows)
Small: Bust is 19.5" (39" around), center length is 25", side length is 30" (Plain 3/4 length sleeve without the gathering at the elbows).