I'm 5'6" and 160 lbs. Medium size fits perfect. I just got it so I don't know how long it will last. Hopefully it doesn't shrink in the wash! So average. Me am 5 6 160 lbs. Shirt is tight. Nice looking shirt. Too tight for a work shirt. If you work with a chainsaw, digging, hauling wood or rock. It's too small. Not enough room in the shoulders. If You have an athletic build. , I ordered a large and will consider that size