For educational and tracking purposes only. Results are estimates and are not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional.
Calculator tool
How this calculator works
Use the explanation to understand the formula, assumptions, and practical limits behind the calculator result.
What This Calculator Does
This calculator gives a starting bra size from the underbust and full-bust measurements you enter. It estimates the band from the underbust and the cup from the difference between bust and band.
Why the Result Is Only a Starting Size
Bra sizing is not fully standardized across brands. Cup volume also changes with the band, which is why sister sizes exist: for example, a 34C and 36B can hold similar cup volume while fitting differently around the rib cage. Stretch, cup shape, strap placement, and breast shape can all change how a size feels in real wear.
Use the result as the first size to try, then check fit: the band should sit level, the center gore should lie flat when appropriate for the style, the cups should not gape or spill, and the straps should support without doing all the work.
Frequently asked questions
Why can two brands give me different sizes?
Brands use different grading, fabrics, and cup shapes. The calculator estimates a starting point, but the final size still depends on how a specific bra is constructed.
What are sister sizes?
Sister sizes keep roughly similar cup volume while changing the band. Moving up one band size usually means moving down one cup letter, such as 34C to 36B.
Should I measure over clothing?
No. Measure close to the body with a soft tape, keeping it level and snug without compressing the tissue. Bulky clothing can shift the estimate.
What should I do if the calculated size feels wrong?
Treat the result as the first size to test. Try nearby sister sizes and check band, cup, and strap fit instead of assuming one number must be correct for every brand.
