Cup Size Calculator – Find Your Cup Letter
Already know your band size? Enter it along with your bust measurement, and we’ll tell you your cup letter – A, B, C, D, and beyond. It’s quick, private, and works for US and UK sizing.
Cup Size Calculator
Your cup letter is C for a 34 band.
Need your full bra size? Try the Bra Size Calculator or convert to international sizes with the Conversion Tool.
What Is a Cup Size?
Your cup letter (A, B, C, D, etc.) shows the difference between your bust and your band. The bigger the difference, the larger the cup. For example, a 1‑inch difference is an A cup, 2 inches is B, 3 inches is C, and so on.
But cup size alone doesn’t mean anything without the band. A 34C is a different cup volume than a 36C. That’s why our calculator asks for both your band and bust – to give you your exact cup letter for your specific band.
How to Use This Calculator
1. Enter Your Band
This is the number you usually see in your bra size (e.g., 34, 36, 38). If you don’t know it, measure your underbust and use our Band Size Calculator first.
2. Enter Your Bust
Measure around the fullest part of your chest. Keep the tape level and don’t pull it tight – it should sit gently on your skin.
Hit the calculate button, and we’ll show you your cup letter instantly.
Cup Size Chart – Quick Reference
Here’s how cup letters match up to the difference between bust and band (in inches):
- 0 – ½″ → AA
- 1″ → A
- 2″ → B
- 3″ → C
- 4″ → D
- 5″ → DD / E
- 6″ → DDD / F
- 7″ → G
- 8″ → H
- and so on…
Note: US and UK cup letters match up to D. Beyond that, they differ – use our conversion tool for exact mapping.
Why Your Cup Size Might Change
Your cup size can change if your weight changes, if you’re pregnant or nursing, or even if you switch bra brands. That’s why it’s smart to measure again every few months. Our calculator gives you a fresh, reliable letter every time.
Sister Sizing – Same Cup Volume, Different Letter
If you know your band and cup, you can find sister sizes – different band/cup combos that hold the same volume. For example, a 34C has the same cup volume as a 32D and a 36B. If your band feels too tight, go up a band and down a cup; if it’s too loose, go down a band and up a cup. Our Sister Size Calculator can help you find these matches.
Not sure of your band size?
Try the Band Size Calculator →Why Trust This Calculator?
- It’s free – no sign‑up, no hidden costs.
- It’s private – all calculations happen locally in your browser.
- It’s accurate – we use the same formula that professionals use.
- We keep it updated – our charts match current brand sizing.
Remember: your result is a great starting point. Because every bra is different, always try on a few styles to see what feels best.
Ready to find your cup letter?
Head back to the calculator above and enter your numbers now.
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