With me it’s skeletal as well. I have a very tapered ribcage, and very broad shoulders compared to my middle. My back starts to get a lot wider right where I measure for overbust even without the more recent muscular additions.
I’ve solved my bra-sizing dilemma, I shop online and wear 28Bs and Cs from British brands. Now I’ve become the bra fitter of all my friends and family. They are of pretty widely varying sizes and shapes, and most of them have a hard time finding anything that fits properly. A bra should be comfortable (a properly sized and fitted bra will not pinch, squeeze, chafe, ride up, or create trenches in your shoulders) supportive, and flattering (and the band has to be nice and snug to hold those puppies up and out, creating the best silhouette) and many struggle to find that within the typical range seen in American stores of 32A/B, 34A/B/C/D/DD, 36B/C/D/DD. Every woman I have fitted has been better served by a different size than they had been buying for years, and 90% of the time the root of their fit issues is that they are wearing far too large a band and too small a cup. If anyone is usually uncomfortable in your bras, I implore you to try going down 1 or 2 band sizes, and up one or two cup letters for every band size you go down. My rule of thumb is to try the band size closest to your actual ribcage measurement, and if it feels uncomfortably tight try the next one up.
I just fitted a friend last weekend. She had been wearing 34Bs (unwired because underwires hurt, unsurprising as the ones she was trying on were 2-3 cup sizes too small and narrow - but I get ahead of myself). She gained weight and her breasts grew a bit recently which prompted her to request my services. She measured 29.5" around the underbust, 35" overbust. By the bullshit ‘add 5’ system she should be wearing a 34A! She was more than a bit surprised to find that 32Ds and DDs provided her with a perfect fit. FWIW, unlike me she has narrow shoulders, no back muscles, and her ribcage is very straight-up-and-down, so much more of her overbust measurement is boobage.
This is actually outdated information, even though most bra companies still tout it. Adding inches to the underbust measurement dates back decades, when bras had much less elasticity. Modern bras, with our Advances in Breastical Technology, are much stretchier and are designed to fit a woman’s body with this in mind. Most women should not add inches to their underbust measurement and most of the remaining women generally only need to add 1-2", not 4-5".
My cite? The bra shop owner that can fit women perfectly and can, just by looking at you (and your rack), go and get 2-3 bras for you to try on and have them all be really damn close, if not right on the money. Oh, and she also worked at bra companies, worked on designing them***, and learned bra-fitting from the lady who fits Queen Elizabeth before opening up her shop.
Is it any wonder 80% of women* wear the wrong size bra, then? And when you watch makeover shows, etc. where women get bra fitted, I’d say about 90-95% of the time, they go down in their band and up in their cup**. Adding those inches for your band size just makes your bra not support the way it’s supposed to.
the oft-touted statistic.
** since a 36C, cup volume-wise, is the same carrying capacity as a 34D.
*** a well-designed bra does the vast majority of breast support in the band, not the straps, which is why it’s even worse than it sounds that so many women wear too large of a band size. And if your straps are digging into your shoulders, leaving dents or welts? You ain’t wearing the right size. And larger cup sizes don’t need a suspension bridge in the back; my G cup bras all lift and support with only two hooks.