Japanese Bra Size to US Converter
A Japanese bra size like C70 is written cup first, then the underbust in cm. Japanese cups usually come out one letter bigger than US cups for the same body, and the band is in cm instead of inches. Example: the same measurements give C70 at Wacoal Japan and 32B at Wacoal America.
Japanese bra sizes: how they are decided
Wacoal Japan uses two measurements, in cm. Band = your underbust, in 5 cm steps. Cup = bust minus underbust, in 2.5 cm steps.
| Underbust (cm) | Japan band | Wacoal US band |
|---|
| Bust − underbust (cm) | Japan cup |
|---|
US and UK cup letters (Wacoal America)
| US | AA | A | B | C | D | DD | DDD | G | H | I | J |
|---|---|---|---|---|---|---|---|---|---|---|---|
| UK | AA | A | B | C | D | DD | E | F | FF | G | GG |
How to measure
- Underbust: measure right under the bust, with the tape level all the way around. Check in a mirror from the side.
- Bust: measure around the fullest part, lifted the way a bra would hold it. Wearing your most comfortable non-padded bra helps.
- Keep the tape snug but don't squeeze, and breathe normally.
Common questions
What is C70 in US size?
Usually about 32B. C70 means an underbust around 70 cm (about 27½ in) and a bust about 15 cm larger. Wacoal America's calculator gives 32B for those measurements.
Why do Japanese cups run bigger?
Japanese brands measure the cup as bust minus underbust in cm, while US brands start the band about 4 inches above your underbust. Same body, different starting point, so the letter shifts.
Does every brand work this way?
No. US sizing in particular varies by brand. Use this as a starting point and check the brand's own chart.