Am normally a size L and ordered an XL just in case. It was way to small and digs in under the arms.
I teach swim lessons where I am in the water up to 8 hours a day during peak season. These rashguards are awesome! I had them in three different colors last season and will be getting more this year. Mind you, I literally wear them daily, all day long in the water.. so it's normal that my swimwear only last one season. I intend to get several more for this upcoming season. I highly recommend!