This calculator estimates bra size from two tape measurements — bust and band (frame) — and reports US/CA, UK, EU (EN 13402), French/Belgian/Spanish, and Australian/New Zealand sizes. A converter maps a listed size in one region to the others. Treat every result as a starting point: try bras on, or get a professional fitting. Brands do not share one grading system.
Signs of a poor fit
Measurement formulas cannot guarantee fit. Research comparing traditional measurement with professional fitting found that absolute size alone was a poor guide. Check the band, cups, straps, and center panel while moving, then try adjacent sizes and the brand's own chart.
Examples
Default 38 in bust, 34 in band
Four inches of difference is cup D on the US/UK/AU scale. The even band is 34. EU uses centimetres, so the same pair is 75 cm E (and 90 cm E in France). Australia prints dress code 12 D. Underbust +4 is 38 D.
41 in bust, 33 in band
The US band even-ups 33 to 34, but the cup still uses 41 − 33 = 8, so the result is 34 H in the US, FF in the UK, G in Australia, and J in the EU — not the 41 − 34 difference.
Convert US 34 D
Index matching (not remeasuring) gives UK 34 D, EU 75 D, FR 90 D, AU 12 D, underbust +4 38 D, and UK dress code 10 D.
Formula
Convert both measurements with 1 in = 2.54 cm. The US/UK band is the truncated inch underbust, then odd numbers step up one so the band is even (the modern +0 method). Sister-size columns (EU, FR, AU, UK dress) round the underbust to a whole centimetre, convert back to inches, round, then even-up — so 32.5 in can print US 32 with EU 75 and dress 10.
Cups use the raw bust − band difference, not the rounded band:
US / UK / AU cup index = floor(bust_in − band_in) starting at AA = 0
EU / FR cup index = floor((bust_cm − band_cm) / 2) starting at AA = 0
Displayed bands (when the US band is at least 28):
US/CA even inch band
UK same band, plus "or dress code {lookupUS − 24}" from US 30
US/CA or UK +4 US band + 4
EU {60 + 5 × ((lookupUS − 28) / 2)} cm
FR/BE/ES EU + 15 cm
AU/NZ dress code {lookupUS − 22} (hidden below US 30)
The converter does not remeasure. It looks up the entered band and cup in that location's table and copies the same index into the other seven lists.
The educational inch and centimetre cup tables on many bra-size pages (AA at under 1 in, or AA at 10–11 cm) are not what the live calculator uses. Match this page to the working tool: AA at a 0 difference, then one cup per inch (or per 2 cm in EU/FR).
Sources
- EN 13402-3 preview — European underbust, bust, and cup-difference sizing framework.
- White and Scurr: Evaluation of professional bra fitting criteria — limitations of traditional measurement and the value of fit criteria.
- Moscarelli et al.: Variation among manufacturers — evidence that cup volume varies across brands.