Bra Size Calculator
Estimate your US bra size from underbust and bust measurements, with the band and cup worked out for you, in inches or centimetres. Calculates in your browser.
Estimated US size
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Show the math
US sizing comes from two measurements:
band = underbust (nearest even in); cup = bust − band
The band is the underbust rounded to the nearest even inch; each inch the bust exceeds the band is one cup letter (1″ = A, 2″ = B, and so on). Sizing varies by brand, so treat this as a starting point and try the bra on. All math runs locally in your browser.
What this does
A bra size calculator estimates your US bra size from two measurements: the underbust (band) and the fullest part of the bust. It works out the band number and cup letter for you.
How to use it
- Measure snugly around your ribcage just under the bust (underbust).
- Measure around the fullest part of the bust.
- Switch between inches and centimetres if needed.
- Read the estimated band and cup size.
How it works
The band is the underbust rounded to the nearest even inch. The cup comes from the difference between the bust and band: roughly one cup letter per inch (1 in = A, 2 in = B, and so on).
band = underbust (nearest even in); cup = bust − band
Understanding your result
Use this as a starting point, not the last word — sizing varies between brands and styles, and so-called “sister sizes” (one band up, one cup down, or vice versa) often fit just as well. Always try a bra on, and re-measure if your weight changes.
Example
A 31 in underbust and 35 in bust gives a 32C.
Sources & methodology
Last updated .
Frequently asked questions
How do I measure for a bra?
Measure your underbust snugly around the ribcage just below the bust, then measure around the fullest part of the bust. The band comes from the first and the cup from the difference between the two.
Why do sizes differ between brands?
Cup and band sizing is not fully standardised, so the same labelled size fits differently across brands and styles. Treat this estimate as a starting point and try the bra on.
Is my data stored?
No. Everything is calculated locally in your browser.
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