I really love this shirt, but had to return it twice.  I usually can wear a med or lg.  They really didn't have an accurate size chart.  The medium was too small in the shoulders so I exchanged it for a lg.  That was still sort of tight - I like a looser shirt.  Returned it again for an XL  and it is perfect.  It keeps me coolat the gym, and I work up a pretty good sweat.  The company was excellant to deal with when exchanging and the merchandise arrived surprisingly fast. Two thumbs up!