Please use this chart as a guideline only. Every gymnast/dancer/athlete is unique and not all of them will fall into every category perfectly. Also, every gymnast/dancer/athlete has their own desired perfect fit. Take into account if your gymnast/dancer/athlete prefers a super tight next to skin "competition" style fit or a little room to grow "comfort" style fit. The girth (vertical torso measurement) is the most important size determining factor.
When in doubt always size up as they can grow into it!