How it works
Bra size is two measurements: the band, which goes around the ribcage under the bust, and the cup, which is the difference between the bust measurement and the band.
- Measure snugly under the bust, level all the way round — that is the band.
- Measure loosely around the fullest part of the bust.
- Subtract the band from the bust: each inch of difference is one cup size (1 in = A, 2 in = B, 3 in = C, and so on).
| Bust − band | Cup (US) | Cup (UK) |
|---|---|---|
| 1 in | A | A |
| 2 in | B | B |
| 3 in | C | C |
| 4 in | D | D |
| 5 in | DD | DD |
| 6 in | DDD / F | E |
| 7 in | G | F |
| 8 in | H | FF |
Sizes are US. Above a D cup the letters diverge, so a US 34DDD is a UK 34E — check which system a label uses before buying.
Examples
Worked examples:
- Band 32 in, bust 35 in: 3 in difference — 32C.
- Band 34 in, bust 40 in: 6 in — 34DDD in the US, 34E in the UK.
- Band 30 in, bust 31 in: 1 in — 30A.
Sister sizes hold the cup volume while changing the band: 34C, 32D and 36B all fit a similar bust. If the band rides up, go down a band and up a cup.
Related: BMI Calculator, BMR Calculator, Bra Size Calculator.
US & Canada Bra Size Calculator: frequently asked questions
- How are US bra sizes different from UK sizes?
- Band sizes match, but cups differ above D: the US usually goes D, DD, DDD, G, while the UK goes D, DD, E, F, FF.
- Should I round my band size up or down?
- Most US brands use even band sizes; if your underbust is odd, try the size above and below and pick the one that sits level and snug on the loosest hook.
- How do I measure my bra size at home?
Measure snugly under the bust for the band and loosely around the fullest part for the bust, keeping the tape level. Subtract the band from the bust: each inch of difference is one cup size.
- What is a sister size?
A size with the same cup volume but a different band — 34C, 32D and 36B all hold a similar bust. Go down a band and up a cup if the band rides up your back.
- Why does my size differ between brands?
Because cup and band grading is not standardised. Use your measured size as a starting point and expect to try a size either side, especially between US and UK labels.