Bra Cup Sizes Explained: A Cup to G Cup
Understand what each cup size means, how they're measured, and find your perfect fit with our comprehensive cup size guide.
How Cup Sizes Are Measured
A bra cup size is determined by the difference between your bust measurement (around the fullest part of your breasts) and your band measurement (snugly around your ribcage, directly under your breasts). Each inch of difference corresponds to one cup letter:
| Difference (inches) | US Cup Size | UK Cup Size |
|---|---|---|
| Less than 1 inch | AA | AA |
| 1 inch | A | A |
| 2 inches | B | B |
| 3 inches | C | C |
| 4 inches | D | D |
| 5 inches | DD (E) | DD |
| 6 inches | DDD / F | E |
| 7 inches | G | F |
This system means cup size is always relative to band size — a 34C has more breast volume than a 32C, even though they share the same cup letter. This is why "sister sizing" works: as the band size changes, the cup letter adjusts to maintain the same cup volume.
Common Cup Size Myths
Myth: DD is Huge
A DD cup simply means a 5-inch difference between bust and band. On a 28 band, a DD cup looks quite modest — roughly equivalent in volume to a 34B or 36A. Many women who think they are a "small B" actually measure as a 28DD or 30D when properly fitted. The perception of DD as "huge" comes from media portrayals, not measurement reality.
Myth: A Cup Means Flat-Chested
An A cup indicates a 1-inch difference between bust and band. On a 38 band, a 38A has the same cup volume as a 32D or 34C. Cup size means nothing without band context. Many women with larger ribcages wear A or B cups and have perfectly proportionate breasts — their volume is simply distributed across a wider frame.
Myth: D Is As Large As Cups Go
Bra cups go well beyond D. Properly fitted bras are available in cup sizes up to K, L, M, and beyond (UK sizing). The idea that "D is the end of the alphabet" comes from mass-market retailers who historically limited their size range. Specialty and full-bust brands routinely carry sizes like 30H, 34J, and 38KK. When you see these sizes on real bodies, they look proportional — not extreme.
How to Know If Your Cup Size Is Right
Good cup fit indicators:
- The underwire should sit flat against your ribcage and fully encircle your breast tissue without sitting on it
- The center gore (the wire piece between cups) should lie flat against your sternum
- There should be no spillage (quad-boob) at the top or sides of the cups
- There should be no gaping, wrinkling, or empty space in the cups
- The cup fabric should be smooth against your breast without cutting in or puckering
If you experience any of the above issues, try a different cup size in the same brand or use our bra size calculator to re-measure. Small adjustments in cup size can make a dramatic difference in comfort, support, and the way your clothes fit.