Bra Size Calculator
Work out your band and cup size from underbust and bust measurements, with the EU band equivalent.
How it works
Band = underbust (in) rounded to nearest even number · Cup letter from (bust − band) rounded to the nearest inch · EU band = underbust cm rounded to nearest 5
A bra size combines two measurements: the band, from the snug circumference directly under the bust, and the cup, from the difference between the fullest bust measurement and that band. Each inch of difference is one cup letter — one inch is an A, four inches a D, and so on. This gives a well-fitting starting point, but styles and brands vary, so trying the calculated size plus its sister sizes matters.
Worked example
An 81 cm underbust is 31.9 in, rounding to a band of 32. A 91 cm bust is 35.8 in; 36 − 32 = 4 in of difference, which is a D cup — a US 32D, or roughly an EU band of 80.
Frequently asked questions
What is a sister size?
A bra with the same cup volume but a different band, reached by going up one band and down one cup (or vice versa) — for example 32D, 34C and 30DD hold a similar volume. If your calculated band feels tight or loose, a sister size often fixes the fit.
The band or the cup — which matters more?
The band. It provides most of the support, so it should sit level and snug around the ribcage without riding up. If the band is right and the cups gape or spill, adjust only the cup letter.
How should I measure?
Measure the underbust snugly and level while exhaling, and the bust loosely around the fullest point without compressing it. Wearing an unpadded bra or none at all gives the most accurate numbers.
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This calculator is for educational purposes. Double-check important results before acting on them.