I bought an XL for my husband but when it arrived, it was a bit tight and made him look like the Hulk, lol. I sent it back, was refunded my money, less shipping, and ordered two of the XXL. Those two shirts arrived Priority Mail whereas the first shirt shipped in about a week. I was very happy with the service, and the extra fast shipping on the second order was a very nice surprise as it was FREE!!As far as sizing, my husband is very big, he is muscular so his back is big as well as his chest and arms. Maybe I should have ordered the XXL but sometimes XL is big enough. So in the end, I don't know if you need to size up because it could have been my bad ordering the too small size.I will say these shirts are VERY nice! They are light and feel like they will be be extremely cool in the hot summer months. They seem to be well made. I haven't washed them yet.I am extremey happy with these shirts and would buy them again and recommend them to anyone looking for a nice looking work shirt that will be good and cool. ?