US · UK · EU sizing
Bra Calculator
Find your real bra size in seconds. Our free bra calculator takes your underbust and bust and returns your band, cup, sister sizes and US/UK/EU conversions — no sign-up, no guessing.
Snug, directly under your bust
Loose, around the fullest point
Sister sizes to try
Same cup volume, different band — handy if the band feels off.
Results are a starting point — fit varies by brand and style.
01The complete fitting guide
Everything in one place — how to measure, the full size chart, what a good fit looks like, fitting tips, and sister sizes at a glance.
02How to measure
You only need a soft tape measure and a well-fitting, non-padded bra (or none at all). Stand up straight and breathe normally.
- Measure your bandWrap the tape snugly around your ribcage, directly beneath your bust. Keep it level and firm. This is your underbust number.
- Measure your bustWrap the tape loosely around the fullest part of your chest, usually across the nipples. Don't pull it tight.
- Enter both numbersPop them into the calculator above. The difference between the two is what sets your cup size.
03Cup size chart
Your cup comes from how many inches your bust is larger than your underbust. Lettering diverges above a D — this is why the same body maps to different letters across regions.
| Bust − underbust | US | UK | EU |
|---|
04Understanding sister sizes
Sister sizes share the same cup volume but sit on a different band. If your calculated band digs in or rides up, the fix is often a sister size rather than a whole new cup.
- Band too tight?Go up one band and down one cup — e.g. 34C becomes 36B. The cup holds the same volume with more room around the ribcage.
- Band too loose?Go down one band and up one cup — e.g. 34C becomes 32D. A firmer band gives most of the support, so getting it right matters.
- Rule of thumbThe band should sit level and snug — you should just fit two fingers underneath. If it rides up at the back, size the band down.
05Common questions
How do I measure my bra size at home?
Take two measurements with a soft tape. Measure snugly around your ribcage directly under your bust for the band, then loosely around the fullest part of your bust for the cup. Enter both above and the calculator does the rest.
How is my band size calculated?
Your band is your snug underbust measurement, rounded up to the nearest even size (most bands come in even numbers). Your cup then comes from how many inches your bust is larger than your underbust. It's the method most fitting specialists recommend — and if the band feels off, the sister sizes in your result let you fine-tune.
What are sister sizes?
Sizes with identical cup volume but a different band. Going down a band size moves you up a cup (34C → 32D); going up a band moves you down a cup (34C → 36B). They're the quickest way to fine-tune fit.
Why does my size differ between brands?
Cup lettering above D is not standardised across US, UK and EU systems, and every brand cuts a little differently. Treat your result as a reliable starting point and try the sister sizes to land your best fit.
How often should I re-measure?
Re-measure whenever your weight changes noticeably, after pregnancy, or roughly once a year. Your ribcage and bust both change over time, and a bra that fit last year may not today.