I'm a size 2 in retailer pretty much across the board - size 26/27 bottom, 2 top, generally go for the xs. and i ordered this in a 4 based on other reviews. it's definitely not a winter coat, which i understood. it's not for layering over a heavy sweater either. i wish i had ordered the size 2 instead so that it was a little snugger in the waist. as is i can wear it over a shirt, dress, or light sweater, and that's fine, but unlike other reviewers i don't think you need to size up if you want the