Cup sizes are proportional to band size. A woman with 30D breasts has about half the breast tissue of someone with 36D breasts. 30D is not large. 36D is average-ish, I think,
I dont know if its different measuring over here in NZ, but at 13, i (and most people I knew around the same age) were only a size A/B cup. D is probably more normal once you're 15/16, although everyone's body is different and grows at different rates. As far as breasts are concerned, i wouldn't be too worried what size they were as long as they felt normal (no lumps or anything) but then, like the others said, its also proportionate to band size (and I'll be honest, i dont understand the american system of that at all - we range from sizes 8-28ish)
The American system is simply the measurement of the spot under your breast (all around), and the cup size is relative to your breast size. That said, no, D is not "average" for a thirteen year old (that would be a/b). However, it is normal.
Guys, cup size is mostly dependent on band size, which is mostly dependent on your build. I'm tall, but I have a small build. A D-cup on me would not be large at all. I'd say 30DD or 30E would be my ideal size. Small, but proportionally small. I'm a 30H. That's proportionally very, very large and causes issues. (Hence why I'm in the process of getting a breast reduction). On a larger person, D-cup breasts would be larger. Check out brabandproject.com. A D cup isn't necessarily huge. I wish I were still a D-cup!
Like others said it really is dependent on band size. But there isnt any true "normal". I was in Ds by 13 and now Im a 32DDD at 17. Compared to some girls thats larger, but in my family thats small. Genes have alot to do with it as well. So you cant really judge it based on others.
Also, I feel like certain parts of the world may having varying averages, at any age but especially at the beginning of puberty. Here in the good ole US of A, we tend to be heavier, even at younger ages. And our avg age of the onset of puberty for girls is statistically lower. So US girls may already be heavier, and be a year into puberty at 13/14 compared to some places. But besides all that, pretty much any size is normal. I was a 38C in 8th grade, and a 42DDD by Senior year. I was 5'2" and 118 lbs. So I was disproportionate as all hell, but still normal. >_<
Quick bra fitting tip: your band size is probably your underbust measurement. Some people (especially if thin or muscular) need to go one band size up. Other people, with more "squish" can go a band size or two down. Your cup size is your bust measurement minus your band measurement. A=1" B=2" C=3" D=4" DD=5" And after that, it really depends on the company. UK sizing is more consistent that US. So, someone who has a 28" underbust measurement and a 32" bust measurement should probably try a 28D or a 30C. Sister sizes are when you go down a band size and up a cup size OR up a band size and down a cup size (to keep everything proportional). This is just a veeeery quick, basic guide. I am not an expert.
well, i am about 6 foot tall and i weigh around 280 somthing and i really couldnt size myself because i have no boobs (remember, my boobs are breast forms i made at home)
I used to work in a lingerie store as an Assistant Manager. Breasts are not in proportion to any other part of your body, so technically you can make them whatever size you want. Even weight doesn't necessarily affect breast size, I've met plenty of women who complained that getting fat didn't make their boobs grow. My best friend and I are about the same size, with her weighing maybe 10lbs more than me at age 13. I was a 32AA and she was 32E. So, put 'em on, if they look right, feel right, wear 'em.