Bra size calculator
Enter your underbust and bust measurements, in inches or centimetres, to get your band and cup size and see it in every major system.
The calculator uses the standard method fitters use today. Your band comes from the underbust measurement rounded to the nearest even number, and your cup comes from how much larger the bust is than the band, at roughly one cup letter per inch. It then translates that US size into UK, EU, France and Italy, since cup letters and band numbers diverge between those systems.
Treat the result as an accurate starting point. Fit varies by style and fabric, so if the band feels loose try one size down, and if the cup gapes or overflows adjust the cup by a letter. For the method behind the numbers, see how to measure bra size.
Calculator questions
How does the bra size calculator work?
It takes your underbust measurement for the band and the difference between your bust and band for the cup. Each inch of difference is roughly one cup size, so a four inch difference is a D cup.
Should I measure in inches or centimetres?
Either works. The calculator accepts both and converts internally. US and UK band sizes are in inches, while EU, FR and IT bands are based on centimetres.
Why is my calculated size different from my current bra?
Many people wear a band too loose and a cup too small. The calculator uses the modern method of rounding the underbust to the nearest even number without adding inches, which often gives a smaller band and larger cup than older advice.
Last reviewed and updated on July 2, 2026. Conversion tables are checked against published international sizing standards.