Bra Size Calculator
Bra Size Calculator finds your band and cup size from simple tape measurements. It also shows sister sizes (alternative band/cup combinations with the same volume). All measurements stay in your browser.
Last updated: July 2026
A bra size calculator estimates your bra size from two measurements: underbust (band) and bust (cup). The difference between them determines your cup size. It also suggests sister sizes — alternative sizes that hold the same cup volume on a different band. All calculations run in your browser.
🔒 All calculations run in your browser. For best results, measure with a soft tape.
How to use Bra Size Calculator
- Measure your underbust (band) circumference in inches.
- Measure your bust circumference at the fullest point.
- Read your band size, cup size and sister size options.
Frequently asked questions
How do I measure correctly?
Use a soft measuring tape. For underbust, measure snugly just under your bust. For bust, measure loosely at the fullest part.
What are sister sizes?
Sister sizes are alternative sizes that hold the same cup volume. If 34C doesn't fit well, try 36B (larger band) or 32D (smaller band).
Is my data stored?
No — all calculations run in your browser. Nothing is saved or uploaded.
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