I'm between a small and medium in regular tops but I got a medium in this top because I took into consideration the activity I would be doing. I was surfing and boogie boarding which requires me to carry a board and reach up/out. So I needed something long enough in the torso that it didn't ride up when I reached. This was perfect.
I'm not a fan of shelf bras and this one has it built in. I wore this top over my bikini so I didn't want any added constraint. It was not too constricting, thank god! I would buy this again in other colors because it did a great job as a rashguard and it stands out from the others.