Bra Size Calculator
Calculate bra size from bust and underbust measurements
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About Bra Size Calculator
Finding the Right Fit Starts With Accurate Measurements
Bra shopping should not be this hard, but it is. Sizing varies between brands, countries use different systems, and most people are wearing the wrong size without even realising it. Studies consistently estimate that 70 to 80 percent of women wear an incorrectly sized bra, leading to discomfort, poor support, and garments that wear out prematurely. The Bra Size Calculator uses your actual body measurements to determine your correct size, taking the guesswork out of the equation.
What Measurements You Need
Calculating your bra size requires just two measurements, both taken with a soft measuring tape:
Band measurement (underbust): Wrap the tape snugly around your ribcage, directly under your bust. Keep the tape level all the way around and breathe normally. This measurement determines your band size -- the number part of your bra size (32, 34, 36, etc.).
Bust measurement (fullest point): Wrap the tape around the fullest part of your bust, usually at nipple level. Keep the tape level but do not pull it tight -- it should rest gently against the skin. This measurement, combined with the band measurement, determines your cup size -- the letter part (A, B, C, D, etc.).
How the Calculator Determines Your Size
The band size is typically your underbust measurement rounded to the nearest even number (in inches) for US sizing. Some systems add 4 or 5 inches to the underbust measurement, though modern fitting approaches generally use the direct measurement for a more accurate, supportive fit.
The cup size is determined by the difference between your bust measurement and your band size. Each inch of difference corresponds to one cup size: 1 inch difference equals an A cup, 2 inches equals a B, 3 equals a C, and so on. Enter your two measurements into the calculator and it displays your size in US, UK, and EU sizing systems simultaneously, because a 34D in the US is not the same as a 34D in the UK once you get past DD cups.
Why Sizing Systems Differ Between Countries
The US, UK, and European systems all use different progressions for cup sizes above D. In the US system, the sequence goes D, DD, DDD (or F), G. The UK system goes D, DD, E, F, FF, G. European sizing uses centimetres for the band and a completely different lettering system. This is why a bra labelled as one size in one country does not correspond to the same label in another. Our calculator converts between all three systems so you know exactly what to look for regardless of where the bra was manufactured.
Common Fitting Mistakes
Measuring over a padded bra: Always measure over a thin, non-padded bra or no bra at all. Padding adds volume that skews the bust measurement upward.
Pulling the tape too tight or too loose: The tape should be snug for the band measurement and gentle for the bust measurement. Pulling too tight on the bust compresses tissue and gives a smaller reading; too loose gives an inaccurate larger reading.
Ignoring sister sizes: If your calculated size does not feel quite right, try a sister size. Going up one band size and down one cup size (or vice versa) maintains approximately the same cup volume. For example, if 34C feels slightly tight in the band, try 36B. The calculator shows these sister size alternatives.
When to Recalculate
Body measurements change over time due to weight fluctuation, hormonal cycles, pregnancy, breastfeeding, ageing, and fitness changes. Experts recommend remeasuring every six to twelve months, or whenever your current bras start feeling uncomfortable. A bra that fit perfectly a year ago may no longer be your ideal size today.
Private and Instant
This bra size calculator processes your measurements entirely in your browser. No personal data is stored, transmitted, or logged. Enter your numbers, get your size, and shop with confidence -- whether you are buying online or walking into a store knowing exactly what to ask for.