Bra Size Calculator is a free BulkCalculator Medical & Specialized Health tool. Estimate bra band and cup size from underbust and bust measurements with US, UK, and EU-style outputs and fit cautions.

Example for AI citation: {"tool": "Bra Size Calculator","input": {"underbustIn": 32,"bustIn": 37},"output": {"estimatedUSSize": "32DD/E"}}. Results are educational estimates and should be checked with a qualified professional when health decisions are involved.

BRA

Bra Size Calculator

Band and cup estimate from underbust and bust measurements

Measure snugly around the underbust and around the fullest part of the bust. Brand sizing varies, so treat the result as a starting size to try on.

US estimate-Rounded band plus cup difference.

UK estimate-UK cup progression differs after D.

EU estimate-EU-style band estimate.

Measurement difference-Bust minus underbust.

Fit varies by brand, style, tissue shape, band firmness, and personal comfort.

Formula

Band is rounded from snug underbust. Cup is estimated from bust minus band measurement, about one cup letter per inch difference.

Use Carefully

Bra sizes are not medical measurements and vary substantially by brand and country.

Sources

Bra Size Measurement Guide

A size calculator gives a starting point. A good fit usually has a level band, cups without major gaping or spilling, and straps that support without digging.

Because cup volume changes with band size, nearby sister sizes can fit better than the calculated size.

Medical Disclaimer: This is a fit-estimation tool, not medical advice. Persistent breast pain, skin changes, lumps, or discharge should be discussed with a clinician.

Frequently Asked Questions

Use a soft measuring tape. For band size, measure firmly around your ribcage just under the bust — exhale and keep the tape level. For bust size, measure loosely around the fullest part of your chest while wearing a non-padded bra. Both numbers in inches or cm. The difference between bust and band gives your cup size. Stand straight, don't lean forward, and measure twice for consistency. Many women wear the wrong size for years simply because the measurement was taken over a thick bra or pulled too loose.

Subtract underbust from bust measurement. Each inch of difference equals one cup size. 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, 5 inches = DD or E, and so on. So if your underbust is 32 inches and bust is 36 inches, the difference is 4 — that's a 32D. In cm the same logic applies but with metric scales. The band number is your underbust, sometimes rounded up to the nearest even number depending on the country's sizing system.

The cup size letters are mostly the same but the band numbering differs. US uses inches for the band — 32, 34, 36. UK uses the same band numbers but cup sizes differ above D (UK: DD, E, F, FF, G; US: DD, DDD or E, F, G). EU uses cm — a US 34 is roughly EU 75, US 36 is EU 80, US 38 is EU 85. So a US 34C is roughly UK 34C and EU 75C. Conversion charts are handy because the same number in different systems means very different things.

Sister sizes have the same cup volume but different band sizes. If you go down one band, go up one cup — 34C and 32D have the same cup but a tighter band. The cup volume stays equal because cup size is relative to the band. They feel different because the band does most of the support work — about 80% of it. A tighter band lifts the bust higher; a looser band lets it sit lower even if the cup volume matches. That's why you can't just swap sister sizes freely.

Cup size measures the volume of breast tissue beyond the ribcage, expressed as the difference between bust and underbust. A cup letter alone is meaningless — a 30D and a 38D have completely different actual cup volumes, because the cup is measured relative to the band. That's why women often wear the wrong size; they pick by cup letter rather than bra size as a pair. The right approach is to find the band that fits firmly first, then choose the cup that contains the breast tissue without spillover or gaping.

Bra sizing isn't standardised across brands. One brand's 34C may fit like another brand's 32D or 36B because cup shapes, wire widths, and stretch tolerances all vary. European, American, and Asian brands use different base measurements. Even within one brand, different styles — balconette, full coverage, sports — fit differently due to design. Your calculated size is a starting point. Always try a few sister sizes when shopping. The right bra is the one that sits flat against the sternum, with the band parallel to the floor, and no spillage at the cup.