Bra Size Calculator

Wrap a soft measuring tape snugly around your ribcage directly under your bust. Then hold the tape loosely across the fullest part of your bust and keep it level. The calculator rounds the underbust to the nearest even band, subtracts that band from the bust measurement, and clamps a negative rounded difference to zero for an AA result. Treat the output as a starting size because brand sizing varies.

Sister sizes share the same cup volume on a different band. If a 34C band feels too tight, try a 36B - the cup holds the same amount of tissue but the band is 2 inches larger. If the band is too loose, try 32D instead. This calculator shows both adjacent sister sizes in the results so you can compare.

Bra sizing is not standardized across manufacturers. Band elasticity, underwire shape, and cup depth vary by brand, so two bras labeled 34C can fit a full cup size apart. Treat your calculated size as a starting point and try several brands before settling on one.

If your bust measurement falls on a half inch, the calculator rounds to the nearest whole inch for the cup difference. Try the resulting size first - most bands stretch slightly with wear. If the band rides up in the back, move to the sister size with a smaller band and larger cup.

US and UK bands use inches (32, 34, 36) and share the same band number, so a US 34 and UK 34 are the same band. EU bands use a standardized centimeter scale from a conversion table, so US 34 becomes EU 75. Cup letters also diverge above D: US DD is EU E, US DDD is EU F, and so on - which is why a US 34DD equals a UK 34DD but an EU 75E.