Find your bra size

Measure your underbust (snug, right under the bust) and your bust (at the fullest point). Your underbust rounded to the nearest 5 cm gives your band size — for example, 74 cm rounds to a 75 band. The difference between bust and underbust gives your cup: roughly every 2.5 cm is one cup letter, with about 12–13 cm corresponding to a B cup. The calculator above does both steps for you and converts the result into EU, UK, US, FR and IT sizing.

Sister sizes have a similar cup volume on a different band length. Going one band down means going one cup letter up (75C → 70D), and one band up means one cup down (75C → 80B). They matter because a style that feels too tight or too loose in the band can often fit perfectly in a sister size — and because some brands simply don't make every size.

There is no single worldwide standard: a 75C in a European brand corresponds to a 34C in UK/US sizing, and on top of that each brand cuts its own patterns — some run a full band tight, others a cup generous. That's why it helps to know your measured size plus your sister sizes, and to adjust per brand. The Cherry Size app does that for 617 brands: free at 3 brands you choose, all of them with a subscription.

The band does most of the supporting work, so it should be snug: level all the way around, two fingers fitting underneath, and it shouldn't ride up when you raise your arms. If it rides up, or you need the tightest hook from day one, the band is too big — try the sister size with a smaller band.

Every 6–12 months, and after anything that changes your body: weight change of a few kilos, pregnancy, breastfeeding, hormonal treatment, or a new sport routine. Bra size isn't fixed — a size that was right two years ago may no longer be.

Yes. The calculation runs entirely in your browser — your measurements are never sent to a server, stored, or shared. There's no account, no cookies used for tracking, and no photos involved. The Cherry Size iPhone app works the same way: everything stays on your device.