According to the CDC, the average teenage girl weighs:
16 year-old - 138.5 pounds
17-year-old girls - 135.8 pounds,
18-year-old girls - 143.5 pounds
While the average for all 16-18 girls is just over 5 feet 4 inches.
So if you want your girl to be to just be Average, then knocking off a little height and adding some weight wouldn't hurt. But if you're going for "well rounded," as in a chubbier girl, 15-20+ pounds might be necessary for someone that height.
But seriously - What kind of story are you writing where all this information needs to be spelled out?
I'm a girl, despite the gender of my avatar.
I'm 5'9'', weight 125 pounds and am a C cup. So yeah, I guess it's realistic. It's not '' average'' since on average, people tend to be shorter and heavier, but it's realistic.
Okay so my main female character is 127 pounds, 5'7 and a 32C. Is this a well proportioned body for a teenage girl?
Not the right place for this, but there is a lot about your character that you have to determine for it to be a 'well proportioned body' for any character.
As it stands, your character's BMI is at 19.9. A lot of places will tell you a lot of different answers. Generally, 18.5-24 is healthy 24-29 is over weight. Anything under 18.5 meets part of the criteria for Anorexia.
Is it really necessary to determine what the weight of your character is? If that is absolutely necessary and you can't figure out if your character's weight is right, google it and look at the images. you might have to wade through a few of them, but there are plenty of people out there with pictures of themselves, how tall they are, and how much they weigh.
That is believable. The rib cage measurement is uncommon for both that cup size and for a taller female, but it does exist. Just not as common. I usually see taller females with a 34 at least. My friend is around those stats and is 36 for the band. She is rather elegant looking. I have seen 32C's here and there, but it is rare so many stores do not carry them. Women's bodies differ so much--it is belieivable. I'd imagine since she is taller and has a ribcage measurement of 32, she has a small frame. For a women that is 5'7, 127 lbs, and small framed, I looked it up and ideal weight happened to be 123--136, so she is within both healthy and ideal range.