What size are 13 year old girls meant to be in bras?

I'm 13 and I'm a 42c and people bully me and say I have extremely over size boobs but I would say a 13 year old should have a bra bout 36b/38b.

You should have the size that fits you. There is difficult to have a chart for girls when they are in puberty because breast size is decided in your genes and the weight can influence as well. if your mom has big ones you can get them too etc but when you get them and how fast they grow is very individual. You have to try in the store and let the staff help you. They know these things. If you get one that don't fit right it can leave marks, hurt and your shoulders and neck can hurt.