I am usually a 00 or 0 in dresses, and i ended up with a 4 in this one. i could barley zip up the 0, and while i could have gotten away with the 2, there is no elasticity in the waistband. the 4 is very slightly roomy, but more comfortable than the smaller sizes on me. for reference, i'm 109-111 lbs, 5'4, and a 30b. 

when i was finally able to wear the dress, i got compliments galore. it really is a beautiful dress! just be sure to size up!