C sits in the middle of the letters people know best, which is why it is so often treated as a fixed size. It is not one. A C is a difference of 3 inches, and what that looks like depends entirely on the band.
What a C cup measures
Take two measurements. The first is snug around the ribcage, just under the bust, which gives the band. The second is loose around the fullest part of the bust. When the second is about 3 inches bigger than the band, the cup is C. A 3-inch difference is a C in US, UK and Australian sizing, and the European system lands on C too.
C cup measurements for every band
| Band | US size | Bust about | UK | EU | AU | Sister sizes |
|---|---|---|---|---|---|---|
| 28 | 28C | 31 in (79 cm) | 28C | 60C | 6C | 30B |
| 30 | 30C | 33 in (84 cm) | 30C | 65C | 8C | 28D, 32B |
| 32 | 32C | 35 in (89 cm) | 32C | 70C | 10C | 30D, 34B |
| 34 | 34C | 37 in (94 cm) | 34C | 75C | 12C | 32D, 36B |
| 36 | 36C | 39 in (99 cm) | 36C | 80C | 14C | 34D, 38B |
| 38 | 38C | 41 in (104 cm) | 38C | 85C | 16C | 36D, 40B |
| 40 | 40C | 43 in (109 cm) | 40C | 90C | 18C | 38D, 42B |
| 42 | 42C | 45 in (114 cm) | 42C | 95C | 20C | 40D, 44B |
| 44 | 44C | 47 in (119 cm) | 44C | 100C | 22C | 42D |
Use the bust column as a starting point. A real measurement rarely lands exactly on a whole inch, and the bra size calculator handles the rounding for you.
Why a 32C and a 40C look nothing alike
Every band size up adds about one cup’s worth of volume. So a 40C does not just have a longer band than a 32C. Its cups are much larger, about the same volume as a 34DDD (UK 34E). If you have ever seen two people who both wear a C and wondered how, this is the reason.
Sister sizes make the link explicit. 34C, 32D and 36B all hold about the same cup volume, and so do 30DD and 38A at either end of the chain. Pick the one whose band fits.
Is a C cup average?
C used to be the size people called average, and plenty of articles still say so. Retailer figures quoted today point higher, around 34DD in the US. But an average is a statistic about other people. What matters is that the band is firm and the cups enclose you without spilling or gaping.
C cup fit problems and fixes
- Spill at the top edge of a T-shirt bra: the cup is too small or too shallow. Try D on the same band, or a balconette in C.
- Gaping at the top: the cup shape is wrong more often than the size. Plunge styles suit breasts that are fuller at the bottom.
- The band rides up at the back: the band is too loose. Go down a band and up a cup, 34C to 32D.
- Straps dig in: the band is not doing its work. Tighten or go down a band before blaming the straps.
The four-point fit check walks through each of these in order.
C cup across countries
The letter C is the same everywhere. Only the band changes: a US or UK 34C is an Australian 12C, a European 75C and a French 90C. The conversion chart covers every band.
Smaller: B cup. Larger: D cup.
Sources & method: sizing rules follow the standard band-and-cup system used by UK, US, AU and EU brands, checked against fitting guides from specialist retailers and fitting communities. How we work.