I am about 5'7 and about 140lbs. The small fit perfectly. It's a little shorter then I thought but it's a beautiful dress and the fabric is better quality then expected!

I first bought the medium and returned it for a small. The medium was just a bit loose at the chest but otherwise perfect. When I got the small, it fit right but was longer than the medium which surprised me. it’s still a pretty dress but would have wanted it to be a little shorter/above the knees.