We suggest finding your perfect sweater size by using your preferred shirt size: 

Sweater Size Shirt Size
Small 14.5 -15
Medium 15.5 - 16
Large 16.5 - 17
X-Large 17.5 - 18
XX-Large 18.5 -19

  Alternately, you can use a chest measurement to help guide your sizing decision. To get your chest measurement, wrap a tape measure under your armpits, around the fullest part of your chest. The tape measure should be snug, neither tight nor loose.  

Size Fits Chest
S 34-36
M 36-40
L 40-44
XL 44-48
XXL 48-50