This product was purchased for my 13-year-old daughter who is 5'4" and 100 lbs. We ordered a size Small. We would have ordered an XS, but there wasn't one available. It is a little bigger than we originally wanted, but it still works, and she can grow into it, too. Initially, she didn't like how loose it was around the waist, so she would wear a black or silver belt with it, which looked nice, too. In the pictures you can see how it is without a belt - flowy and comfortable. The material is thinSee full review