Pletny of room
I picked up the Ex Officio Air Strip Lite Shirt for a canoe trip and it worked perfectly for keeping the sun and wind off all week. It breathes well, handles all sun, and has a number of features that seem small but add to the shirts functionality. I especially like the double collar for protecting your neck. The shirt is REALLY cut generously. This is great in the morning when you want to throw a base layer on under it and does help with keeping you cool, but if you are in between sizes, I'd say go smaller.