How big should a 13 years old boobs be

Something else my sister wants to know.

It has to be almost adult size but firm. If its small get used to it, its probably going to remain that way.

There is no standard boob size for any age, for each of us is different in terms of growth rate, and also all our boobs start growing at different ages and times, and will also reach different maximum sizes.

So the answer is: There is no standard boob measure with age.

Thank you.

Depends on diet, weight, and genetic (?) makeup. There are many things to worry about than boob sizes.

I don't know what motivates the question but I'd like to say, if appropriate, let it be don't be too bothered about how it should measure up to the next 13 year-old.

A/B cup, unless you are fat.