When I first bought this, I ordered a medium. I found that it was smaller than I was expecting, so I ordered a large this time. Definitely glad I tried the large because it's more flattering and is very comfortable.
I'm usually a size 8/10 in tops, and I found the medium was the best fit (flattering but not tight). If you like it loose, order a large.
This is the softest and most comfortable shirt...I absolutely love it and would recommend it to others.