Bra Cup Size Guide: AA to K and Relative Cup Sizing
Understand why cup letters are relative to band size, how common US, UK and EU cup progressions differ, and why a bra size is only a starting point for fit.
Cup Letters Are Relative to Band Size
A cup letter does not describe an absolute breast volume. The same letter on different band sizes represents different cup dimensions. This is why sister sizes move diagonally through a sizing system rather than keeping the same cup letter.
Common Cup Progressions
The table below is a simplified reference for the measurement-difference method used by this site. Real commercial sizing systems can vary, so it should not be treated as a universal brand chart.
| Approx. Bust–Underbust Difference | US / Canada | UK | EU |
|---|---|---|---|
| 1" | A | A | A |
| 2" | B | B | B |
| 3" | C | C | C |
| 4" | D | D | D |
| 5" | DD | DD | E |
| 6" | DDD / F* | E | F |
| 7" | G | F | G |
| 8" | H | FF | H |
| 9" | I | G | I |
| 10" | J | GG | J |
*US cup lettering varies among manufacturers; some use DDD, some F, and some use both. UK double-letter progression also applies differently across manufacturers at extended cup sizes.
What This Chart Can and Cannot Tell You
A measurement-based result is a useful starting point, not a guarantee of fit. Research comparing traditional measurement with professional fit criteria found meaningful differences between calculated and best-fit sizes, supporting the use of garment fit checks alongside measurements. citeturn1search0
Frequently Asked Questions
Answers about sizing methods, measurements, and fit considerations.
Is a D cup always the same size?
No. A cup letter is relative to the band. A 28D and 34D do not represent the same physical cup dimensions. Sister sizes can have similar cup capacity, but cup shape, wire width and construction also change.
Why do US, UK and EU cup letters differ?
The systems use different letter progressions, especially after D. Use the target manufacturer's chart when converting a size rather than assuming that the same letter has the same meaning everywhere.
Sources & Standards
- White & Scurr (2012), Ergonomics, DOI 10.1080/00140139.2011.647096
- ISO 8559-1:2017, Size designation of clothes — Part 1: Anthropometric definitions for body measurement