How big are your breasts supposed to be at 13?

Answer 1

This all depends on the individual girl. Some girls will have already developed breasts by the time they are 13, and other may not have even started. This is regulated by when / how long you have been going through puberty for. Generally, most girls who are 13 are around a A- to a B-Cup. Mind you, some can be as large as a D-, while other might be smaller than a AA-Cup. There is really no "normal" standard for this.