I'm sure you've heard all of these, but unfortunately, it's not very helpful when determining what bra size they're referring to. Cup size is extremely separate from band size. Those 2 numbers/letters together is what makes a bra size.
Telling someone you are a C cup is like telling them to draw a rectangle and only saying that it's 4" long. It is not enough information!
A 28C is going to have extremely different cups than a 38C or a 48C. The chart below shows the different sizes for different breast volumes. A 28C would be about 240cc, while a 48C is 1580cc!