During my bra fitting days, the question I heard most often was: “Will this go on sale?” But the next most popular expression (and most relevant to this article) was: “I’m a what?!” Usually this occurred after curiosity compelled the client to ask what bra sizes they needed. “No, I can’t possibly be a (fill in the blank) cup!” Sound familiar? There’s plenty of blame to go around for this confusion: celebrities and influencers, the media, poor training for department store fitters, plastic surgeons, and generational misunderstanding repeatedly passed onto the next person. As a result, cup sizes follow a cookie cutter template related to size:
A’s are flat, B’s are small, C’s are average, D’s are big, DD’s are huge, DDD’s are insane
And any further down the alphabet? Well, you are clearly ginormous. Putting aside the icky objectification of bodies and use of negatively charged adjectives to describe breasts in general, the truth is cup size means absolutely nothing on its own. Cup sizes are only one half of an old married couple, and it is their long-suffering partner, the band size, that gives the cup size any kind of significance. Cup sizes vary widely from one band size to another, i.e., a D is not a D is not a D.
Bras, like other fashion items, are built on the idea of scaling proportions, but the scale does not center on the cup: It’s all about the band. The band of the bra represents your torso girth, and everything from the width of the cups to the placement of the straps to the length of the wings shifts with each size to customize the fit. As you step up in band size, the entire bra scales upward because the designer recognizes that the person wearing this band is proportionally bigger than the person who wears a smaller size. Thus, if a person wears too big a band size, fit issues ensue, such as the underwire extending too far on the sides, the band not snugly supporting the breasts, the straps being too wide set, and proportionally larger cups requiring a smaller size to fit.
How do cup sizes factor in? They follow a straightforward formula. (Note: Some European brands scale each cup size by centimeters instead of inches.)
A = Band Size + 1″, B = Band Size + 2″, C = Band Size + 3″, etc.
Because there is often a limited selection of sizes available, people will buy “cup size equivalent” bras—or bras whose sizes are different but whose cups require the same amount of breast tissue to fill them. This phenomenon is also known as “sister sizing.” For example, all of these UK bra sizes are cup-size equivalents or sister sizes:
28G = 30FF = 32F = 34E = 36DD = 38D = 40C = 42B
In American sizing, they equate to:
28I = 30H = 32G = 34DDD = 36DD = 38D = 40C = 42B
And here is the heart of why cup sizes mean absolutely nothing without a band size to define them. The person who wears a 28DD, for example, has less breast tissue than the person who wears the 34DD. In fact, a 34DD is cup size equivalent to UK 28FF or US 28H!
To demonstrate how the band and cup size work together, let’s examine the DD cup. Below are some sample measurements for a person who might wear these sizes:
28DD = 28″ ribcage, 33″ chest
30DD = 30″ ribcage, 35″ chest
32DD = 32″ ribcage, 37″ chest
34DD = 34″ ribcage, 39″ chest
As you can see, each DD cup represents not only a completely different set of measurements but also a completely different sized person. However, I do want to note that some people choose to size up in the band for comfort or health reasons. For example, the person measuring a 28DD may actually prefer a 30 or 32 band, making the new cup size a 30D or a 32C.
The Moral of the Story: Cup size cannot and should not be used as way of representing breast size. All that matters is you find the bra size that fits, flatters, and feels comfortable to you!
For more information on how band and cup sizing works, please check out my fitting guide and the video below: