I got an extra large because of what the review said, I'm typically a large in tee shirts.  Wish I would have gotten my normal size.  I'll be giving this to my big brother and buying a smaller size.  I honestly think even a medium would fit me.  I would get your true size or a size smaller, but definitely don't size up!!!  That's just crazy, I'm not sure where people are getting that idea from.  The material of this shirt by the way is AMAZING!!! SOOOOOOO soft and the material seems very sturdy. Not cheap at all!  It did take awhile to receive but less than they said it would and it was definitely worth the wait!