I was lucky enough to come across a great sale for these locally so was able to try them on and picked up quite a few cheap (after spending $$ for my first one). However what I found was that while my first one fit perfectly at M ( and the L I tried seemed huge), I turned out to be very much an L in a very similar top (round vs v neck) and an M in others. I think Boob may have varied the cut a bit year to year. Is there anywhere you could try some on? Or maybe order a couple in different sizes and later exchange one for the right size? I *love* these tops by the way, they are so simple, flattering and have saved my ability to leave the house while breastfeeding (I'm pretty large breasted and discretion is literally impossible with any other nursing top style I've tried or with a cover - my son just plays/gets impatient with it on his head). Good luck!