I am a size 10/12, and usually take a size L in tops. Based on comments below I bought the XL and it fits well. I got the "Heather Spruced" color and the arms fit fine and the material is a nice weight. This isn't a slimming top by any means, but it is so comfortable I don't care! It isn't something I'd wear to work (I am a college professor), but this is casual wear at its best.
I love this! I swear, this sweater is contagious. Once you wear it, several people will ask where you got it from, and purchase the same one. It's so flattering and comfy, I purchased 2 different colors. Really can't go wrong.