How to measure your size.
With arms at sides, place a tape measure under your arms and run it around the fullest part of the bustline and across the shoulder blades.
B) SHOULDER TO SHOULDER
The Shoulder to Shoulder measurement is taken ON THE BACK from one end of the shoulder to the other. Do not pull a straight line from these two points; follow the natural curve of the body.
The Jacket Sleeve measurement is from the end of your shoulder to the wrist. (Not to be confused with "Shirt Sleeve" which follows the "Center to Cuff" measurement.). This measurement should be close to the length from a jacket's shoulder seam to the end of its sleeve.