Ralph Lauren clothing sizing is vastly different from size to size. I would probably say the difference between each size in chest for any sub brand is 4 inches. Ex) XS in a shirt would be a 36 chest whereas a S would be 40 chest. I own Rugby, POLO and RRL stuff. I'm a small in all 3. If I went XS, it would be too tight. Brands like Apolis have 2 inch chest size difference. Ralph Lauren shirts have 4 inches in chest size difference.