it is normal, although they are a matched pair, they both grow and preform their function separately so their growth patterns will not match exactly. even after they have finished developing they will be slightly different. Most of the time the difference is so small it is not noticeable.
You may also notice people have one leg slightly longer than the other (that's why people lost in the desert often walk in circles) they will have one arm longer than the other, etc. unless you can tell from across the room, don't worry about it.
fer sure i agree with janice, mine aren't equal and i'm not even in puberty i think it follows the one hand is bigger than the other, one leg is and one foot. and yes i also agree with if they are signifiantly differnt then be a little concerned and get it checked
You'll find that a loto f girls actually have uneven breasts, no person is perfectly symmetrical. You breasts can grow at differently. It's nothing wrong though, unless they are severely different then I would advise you to get it checked just in case.
Yeah what Janicee said, but seriously girls breast are never the same size, even when they are older, it isn't always noticeable but everyone has one larger and one smaller then the other.
Even after puberty you will still notice one more bigger then the other one. Just like our one foot is slight bigger then the other one. We aren't as even as some people think we are
It's not just girl going trough puberty, all girls have breasts that are not the same size, some have it more noticible than others but then that is just another detail.