Bra Size Calculator
Measure underbust and bust, get your band and cup for US sizing plus UK, EU and FR equivalents — with sister sizes and both band-method conventions.
| Bust − underbust | 1" | 2" | 3" | 4" | 5" | 6" | 7" |
|---|---|---|---|---|---|---|---|
| US cup | A | B | C | D | DD | DDD | G |
| UK cup | A | B | C | D | DD | E | F |
| EU cup | A | B | C | D | E | F | G |
How to use
- Measure snug under the bust, keeping the tape level — that is the underbust.
- Measure around the fullest part of the bust without compressing.
- Enter both in centimeters and read your US size, UK/EU/FR equivalents and sister sizes.
- If another site or chart disagrees, switch the method toggle — legacy “+4” charts read 2–4 cup letters smaller.
Frequently asked questions
How is band size calculated?
Modern fitting (the default here) uses the underbust directly: convert to inches and round to the nearest even number — that is the US band (30, 32, 34…). Professional fitters and most current brand charts work this way because a snug band on the loosest hook is what actually supports. The legacy “add 4 inches” method survives on many older charts, so the tool offers it as a second method — see below.
Why do other sites give me a completely different size for the same measurements?
Almost always the band method, not your tape. Example: underbust 73 cm, bust 88 cm. Modern direct fitting: band 28", difference 5.9" → 28DDD (US). The +4 method: 28" + 4" = 32" band, and the cup letter is read against the wider band → 32B. Both are internally consistent conventions for the same body — 32B simply assumes a looser band. Pick the method your brand’s chart uses, then stay with that brand’s scale.
How is the cup letter determined?
The difference between bust and underbust, in inches: 1" = A, 2" = B, 3" = C, 4" = D, 5" = DD and so on. A cup letter alone means nothing without the band it is paired with — the letter is relative to the band, which is exactly why the +4 method reads smaller letters for the same breasts.
What is the difference between US, UK and EU cup labels?
Up to DD they agree. Beyond that the alphabets diverge while the actual cup volume ladder is the same: US DDD = UK E = EU F, US G = UK F = EU G, US H = UK FF = EU H. EU (and FR) bands are also counted in centimeter steps of five (75, 80, 85…) instead of even inches. The calculator lists US, UK, EU and FR equivalents for you.
What are sister sizes?
Bras with the same cup volume on neighboring bands: one band down pairs with one cup letter up (34C → 32D), one band up with one letter down (34C → 36B). The calculator lists both sisters for your measured size — useful when the band feels tight or loose but the cups fit.
Which size should I actually buy?
Start from the method your brand uses, fit the band snug on the loosest hook, and use the sister size to fine-tune. Sizing varies by brand, style and fabric — when a brand’s own chart differs, follow the brand.