Breast Size

What is the average breast size for a 13 year old girl?

Reply:

It would be very misleading to give you any ‘size’ as this depends largely on the state of your puberty.
Some girls start it earlier while some only a few years later.

That would mean a 13 years old may have larger breasts as a 17 year old one if she started puberty sooner.
But breasts are genetic, it depends what genes you inherited. Each person has a different size.
On top of it, it is also depends on race.

You are young and you need to wait to finish your puberty. It is impossible to rush the nature.
The most common cup size is 34B (for adults).