US sizes. NOTE: Please order the size shown in the product description on the left side (not the Amazon size chart), the size information in the product description is accurate. Classic flannel shirts with Western styling. Everybody wants to know where got it. Must have Christmas gift. It very comfortable to wear relaxing or doing stuff in yard or campsite and for use in all types of outdoor activities from camping and sitting around a fire, taking a walk. Pearl snap design, easy on and off.