Bra Size Calculator
Find your bra size in US/UK and European (FR/BE/ES) sizing from your underbust and bust measurements. Supports both inches and centimeters.
About Bra Sizing
Bra sizing consists of a band number (your rib cage measurement, rounded to the nearest even number) and a cup letter (determined by the difference between your bust and band measurements). A 1-inch difference equals an A cup, 2 inches a B cup, and so on. Sizing conventions vary significantly between countries — US and UK sizes use the same letters but different band numbers, while European systems use centimeter-based bands. For general health measurements, our BMI Calculator can help assess body weight relative to height.
The "sister size" concept means that adjacent band/cup combinations offer the same cup volume — for example, 34C and 36B contain the same volume. If a bra doesn't fit well in your calculated size, try the sister size with a smaller band/larger cup or larger band/smaller cup. To find your height in different units, our Height Calculator converts between centimeters and feet/inches instantly.
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For a related calculation, use Height Calculator to convert height between cm and ft+in, or predict a child's adult height using mid-parental formula. Alternatively, use Conversion Calculator to convert units across Length, Weight, Volume, Temperature, Area, Speed, Pressure, and Energy.
For the underlying method, read Unit Conversion Guide: Metric, Imperial, and the Math That Connects Them.