I am a size 10 top. On reading the other reviews, I ordered both a size 12 and a size 14. The 14 fits very nicely, in a flattering fitted but not skin-tight way - it is, however, still very snug.
I like the breathable back and that the short-sleeves are a decent length (covers armpits rather than armpit length, so fabric seams will not rub them). I am hopeful that this will be suitable wicking-layer for my 100km charity walk!
Worth noting: the red is more an orange-red (as opposed to a postbox-red).
UPDATE Also worth noting: It shows sweat.