Yes, "C" is a standard bra cup size, but it doesn't refer to a fixed measurement on its own—it represents the difference between two measurements: the band size (measured around the ribcage, under the bust) and the bust size (measured around the fullest part of the bust).
Cup sizes are lettered—typically A, B, C, D, DD/E, DDD/F, G, and beyond—with each letter representing roughly a 1-inch (2.5 cm) difference between the band and bust measurements. For example:
- A cup: about 1 inch difference
- B cup: about 2 inches difference
- C cup: about 3 inches difference
- D cup: about 4 inches difference
So a "C cup" means there's roughly a 3-inch difference between the underbust (band) measurement and the bust measurement at its fullest point. Importantly, cup size is relative to band size—a C cup on a 32 band is a different physical volume than a C cup on a 38 band, even though the letter is the same. This is why bra sizing is always written as a combination, like "34C" or "36C," with the number indicating band size and the letter indicating cup size.
Sizing conventions can vary somewhat between countries and manufacturers (for instance, UK, US, and European sizing systems don't always align perfectly), so a C cup from one brand or region might fit differently than a C cup from another. Because of this variability, many people find it useful to get professionally measured or try on multiple brands to find their best fit, rather than assuming the letter size will be consistent everywhere.
In short, yes—C is a cup size, sitting between B and D, but its actual meaning depends on the band size it's paired with.