I currently sell Men's Ralph Lauren Purple Label.  I receive a lot of questions about sizing.  The following information is from the Ralph Lauren Purple Label sizing chart for Men's Shirts and Sweaters, that I obtained directly from Ralph Lauren.   I hope that it is helpful when you are shopping for Men's Ralph Lauren Purple Label sweaters and shirts. 

US Size        S                      M                       L                    XL                  XXL

Chest        34"-36"           38"-40"           42-"44"           46"-48"             50"-52"

Neck       14"-14 1/2"    15"-15 1/2 "   16"-16 1/2"    17"-17 1/2"       18"-18 1/2" 

Waist        28"-30"           31"-34"           35"-38"           40"-42"             43"-45"