Men of Lemmy, how old were you when you found out that bra cup sizes are not standardized in the slightest?
It's so bad that my fiancée has some bras that say she's a B cup and others that says she's a D cup. In order to go bra shopping, you have to actually try them on to find out if they fit.
If I had to try on underwear to see if they fit, I might not bother with underwear at all!
Most of the bras that my girlfriend gets fits on her first try, although she does tend to prefer sister sizes over her real size. If your girlfriend is having issues with bras fitting, it might be worthwhile to read up on how bra sizes are actually calculated and do a measurement yourself. Funny enough, most girls don't seem to know how the bra size system works either and they just get their sizes through trial and error, which seems like what has happened here.
The letter by itself is fundamentally meaningless. A 32D is equivalent to a 34B! And most girls severely underestimate their actual size. What would colloquially be called a B or C is actually an E
I don't think you know how the bra size system works. The number is the size measured underneath the breasts. The letter is the cup size determined as a the difference between the measurements across and underneath the breasts.
Therefore no way is 32D equivalent to 34B. Or at least it shouldn't be equivalent, but manufacturers don't respect the standard, so the equivalence is not impossible in some cases. It's really super inconsistent.
Also breasts can have different shapes and can be placed closer or further appart, which makes finding a fitting bra very hard for some people.
You can add numbers correctly, but why the hell would you do that?
Adding cup size to band size is a bit like buying pants and adding leg size to waist size. One measure cannot compensate for another.
A woman with band size 32 measures 32 inches around her torso underneath her breasts. That's the number she needs, or else the bra is going to be too loose or too tight under the breasts.
A woman with small breasts and large chest cannot buy a bra with tighter band size that she wouldn't be able to put around her chest and compensate with bigger cups. That would mean she would have to leave the bra open in the back and wear it as a strange kind of napkin with huge cups hanging loosely on her small breasts, leaving a large room above them.
The same goes for a woman with large breasts and thin chest. If she bought a bra with bigger band size and compensated with smaller cup size, it would be very loose around her chest and there would be two funny little cups resting on the top of her much larger breasts.
I'm taking it into caricature territory to make it easier to imagine, but even if the differences in size are not that big, it's kind of what it actually feels like for a woman.
You’re close! Both a 34B and a 32D would have the same measurement around their bust, but the bust size alone can’t be used to determine bra size. The rule is to increase band size by 1 increment (which is 2”) and reduce cup size by 1 increment (the letter) to maintain the same volume.