It depends on how fat she is. If she is thin yet still has monster jugs, her cup size could be pretty big. At the same time, she could just as easily be very small breasted, yet fairly large around the top. It all depends. :dunno:
Female body shape can have a lot to do with it. "Fat" is fairly non-descriptive.
Apple and hourglass shapes tend to have a larger chest diameter than straight or spoon/pear shaped, at least in proportion to their hips. Doesn't mean their cup size is bigger though, although sometimes it is in proportion. And added weight is not a guarantee of increased cup size, especially with straight or, even more so, spoon/pear shaped.
99cm, to get the actual size you divide it by 2.54 to give you the size in inches.
99= 38. 9, so that would be around a C cup.
Chest diameter and cup size are unrelated, aren't they? For example, if you measure underneath the breasts, you will get the true chest size. Say 34"/85cm
Then, you measure over the breasts and get, obviously, as larger diameter. Say 37".
Subtract the 34 from 37 and get 3 inches. A three inch difference is a C-cup. (and so on)
This approach is only accurate to C cups. Once you hit D cups or larger, it's hard to measure, or with aging women and more sagging, the same is true.
There are also variations between manufacturers. Some cater to normal sizes, whereas full figured styles tend to have more volume for the same cup size.
Fredrick's of Hollywood maintains this size chart:
http://www.fredericks.com/Help91/Help91,default,pg.html#chart5
If you to visit, say, a Lane Bryant, the chart would differ greatly.
Herroom has some information on other comparisons:
http://www.herroom.com/bra-fitting-advice,901,30.html
http://www.herroom.com/full-figure-bra-cup-sizing,905,30.html
Frankly, if I was going to start a bra line, I would add more than just the chest-to-bust measurement. I would also add:
- Width of each breast (which often varies)
- Width between the breast (split, which does vary, significantly sometimes)
- Total volume and weight (which can be estimated by adding the hang of the breast), which will always vary
And build a custom bra for a woman. Many women wear bras that are very uncomfortable because the bra cup itself starts too far inside or not far enough, and the outside starts to early or late. There are all sorts of adjustable bras, but they never adjust enough. It completely sucks (possibly even dangerous) for a woman to have an underwire to poke their chest or the outside of their bust. And there are non-underwire solutions that work well, but most don't cater to.
There is no "magical bra" that works for every woman at the allegedly same dimension+cup size. It should be fitted or at least customizable into a range that matches their different breast split, width and volume. I've modified my wife's bras (yes, I sow
) to fit her better. I've also modified her underwires (a half-underwire is often enough -- just for the outside support).
One of these days my dream engineering job will come true.