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!
There are plenty of brands that follow mostly standard sizing, as I understand it. But popular brands in the US (like Victoria Secret) generally don’t.
I fell down the r/abrathatfits rabbit hole one day, years ago. It’s fascinating.
I once talked to my girlfriend about bra sizes and how much i don’t understand them. Then we both googled bra sizes and how often women wear the wrong size and fit and all. It’s a whole science behind it and it’s quite interesting. Now, 10 years later i still often think: oh no, she wears a bra that doesn’t fit right and probably doesn’t even know it.
Yup! “Oh, she should probably go down a band size and up a cup size” popped into my head one day and I laughed at the absurdity.
I introduced my wife to the world of proper bra fit, because she’d never known any of it. No one taught her. Made me feel vaguely guilty of mansplaining, but it helped!