We ordered a size 9 for my neice and a size 6 for my daughter. They were both huge! My neice ended fitting the 6 perfectly. I ordered a 4T and my size 6 seven year old can wear it - the straps are still a little long but we can fix that.Other reviewers said order a size down. We had to order TWO sizes down. These girls are both very narrow framed so that might make a difference.