You will be a d cup or double dd
well it matters what size you are
34b is bigger.
There are some females fully grown with same size or even bigger.
You should were thin bras so as to keep your breasts safe and be sexy.
At this age your breasts are still developing so don't worry about your size, becasue all women come in different shape and sizes. When I was 13 I was a size 34B.
Size 34B
34B
34b
34B
34B
34B
34B is the equivelant to 12B in most bra sizes. Which is roughly 35". It usually means you have a smaller back rather than breast size. this size is a good size, not to small and not to big , 34b is actually a common size , many people have this size