About this tool
The Bra Size Calculator turns two tape measurements — your underbust (band) and your fullest bust — into a recommended bra size, with US, UK and EU equivalents and sister sizes. It runs entirely in your browser and stores nothing.
Measurements in centimetres are first converted to inches. The band is your underbust rounded to the nearest even inch, and the cup comes from the difference between bust and band: each inch of difference steps up one cup (0 in = AA, 1 = A, 2 = B, 3 = C, 4 = D, 5 = DD, and so on, with the exact letters depending on the US, UK or EU system). EU bands are the band in centimetres rounded to the nearest 5 (65, 70, 75, 80…). Sister sizes keep the same cup volume by moving one band up with one cup down, or one band down with one cup up.
This is general guidance only, not a professional fitting. Cup lettering and fit vary noticeably between brands and countries, so treat the result as a starting point and try styles on where you can.