Bra Size Calculator
Find your true bra size from band and bust measurements. Includes US, UK, EU sizes plus sister sizes for alternatives.
LIFESTYLEFind your true bra size from band (underbust) and bust measurements. Returns US, UK, and EU sizes plus sister sizes for finding alternatives when your main size does not fit a particular brand.
Band size = nearest even inch under your bust. Cup size = (bust - band) in inches: 1 = A, 2 = B, 3 = C, 4 = D, 5 = DD/E, 6 = DDD/F, 7 = G. Avoid the older "+4 method" - it almost always gives a band too loose. Sister sizes share cup volume but different bands: a 34C is the sister size of 32D (smaller band, one cup up) and 36B (larger band, one cup down).
Bra Size Calculator
Find your true bra size from band (underbust) and bust measurements. Get your US, UK, and EU sizes plus sister sizes for finding alternatives.
Sister Sizes (try if main does not fit)
Fit Tips
- The band should sit level around your body and feel snug - it provides about 80% of the support.
- Cups should fully contain breast tissue without spillage, gapping, or quad-boob.
- Center gore (between cups) should lie flat against your sternum.
- Straps should hold without digging or sliding off - if you tighten straps to lift, the band is too big.
How Bra Sizing Works
Bra size is a band number + cup letter. Band size is your underbust measurement rounded to the nearest even inch (in the US) - 32, 34, 36, etc. Cup size is the difference between bust and band: 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, 5 inches = DD/E, 6 inches = DDD/F, and so on.
US, UK, and EU sizing all use similar cup-letter logic but the band numbers differ. A US 34D ≈ UK 34D ≈ EU 75D. The biggest pitfall is the "+4 method" from older US fitting guides, which adds 4 inches to your band measurement - this almost always gives a band that is too loose. Modern fitters and bra makers (ThirdLove, True&Co, Rigby & Peller) recommend measuring your true underbust and rounding to the nearest even number.
"Sister sizes" share the same cup volume but different band sizes. If a 34C does not fit, try 32D (same volume, smaller band) or 36B (same volume, larger band). About 80% of US women wear the wrong bra size; a proper fitting often goes 1-2 band sizes down and 2-3 cups up from what people are wearing.
Sizing is a starting point - actual fit varies by brand and style. Many specialty shops offer free in-person fittings.