Bra Size Calculator
Recommended bra size from underbust and bust measurements, with sister sizes.
Formula
Band ≈ underbust + 4-5″ ; Cup = bust − band
How to use
- 1Measure your underbust snugly and your bust loosely.
- 2Enter both and choose inches or centimetres.
- 3Pick the traditional or modern method.
- 4Read your recommended size, UK and EU equivalents, and sister sizes.
About this calculator
The most common reason a bra feels wrong is the wrong size, and many people wear one for years. Two measurements get you close: the snug reading under the bust and the fullest reading across it. This calculator turns those into a recommended band and cup, shows UK and EU equivalents, and lists sister sizes as a proper fitting-room starting point.
Formula explained
Measure the underbust snugly and the bust loosely. Traditional method: Band ≈ underbust + 4 to 5 inches. Modern method: use the underbust more directly, rounded to the nearest even number. Cup = bust − band, where each inch of difference moves the cup up one letter (about 1 in = A, 2 in = B, and so on).
Worked example
Traditional: band ≈ 30 + 4 = 34. Difference 36 − 34 = 2 inches = a B cup, so about 34B. Try the sister sizes too, since fit varies by brand.
Tips & notes
- Measure without padding and keep the tape level; a tilted tape skews everything.
- Judge the band first - it provides most of the support and should sit level and firm.
- A too-loose band usually calls for a smaller band and a larger cup, one of the sister sizes.