These are a pretty true fit. They are tapered right around the mid-section so if you are in between sizes, go up. They are meant to be worn a little loose. 
6.1-ounce, 100% ring spun cotton
Soft-washed, garment-dyed fabric
Double-needle collar
Twill-taped neck and shoulders
Twill label
Double-needle armhole, sleeve and bottom hems