Bra Cup Size Calculator
Enter your measurements below to estimate your bra band and cup size. Use a soft measuring tape and measure in front of a mirror for best accuracy.
How to Measure Cup Size Correctly
If you've ever wondered why one bra feels perfect and another in the same labeled size feels uncomfortable, you're not alone. Bra sizing can vary by brand, style, and even fabric stretch. A reliable starting point is learning how to measure cup size and band size at home.
This calculator helps you estimate your size using two key numbers: your underbust and your full bust. Once you have those, you can determine a likely band size and cup letter.
What You Need Before Measuring
- A soft measuring tape (tailor's tape works best)
- A non-padded bra or no bra
- A mirror to check tape position
- A notebook or phone to record measurements
Step-by-Step: Measure Your Bra Size at Home
1) Measure Underbust
Wrap the tape around your ribcage directly under your bust. Keep it horizontal and snug (not painfully tight). Exhale gently and record the number.
2) Measure Full Bust
Wrap the tape around the fullest part of your chest (usually over the nipples). Keep tape level and comfortably loose—not compressing the tissue.
3) Calculate Band Size
Most modern sizing methods use your underbust as the base. This calculator rounds to the nearest even number for your band (for example, 31.4 becomes 32).
4) Calculate Cup Size
Cup size is determined by the difference between your full bust and band size. Each inch of difference usually represents one cup step.
| Difference (inches) | Estimated Cup |
|---|---|
| 0 | AA |
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD / E |
| 6 | DDD / F |
| 7 | G |
Understanding Sister Sizes
If your calculated size feels close but not perfect, try sister sizes. Sister sizes keep similar cup volume while changing band tension.
- Go down one band size and up one cup (e.g., 34C → 32D)
- Go up one band size and down one cup (e.g., 34C → 36B)
Common Measuring Mistakes
- Measuring over thick clothing
- Letting tape tilt up or down in the back
- Pulling tape too loose at the underbust
- Assuming all brands use identical cup grading
- Not re-measuring after body changes (weight, hormones, pregnancy, training)
How to Check Fit After You Calculate
Band Fit
Your band should feel secure on the loosest hook when new. It should stay level and not ride up in back.
Cup Fit
Cups should fully encapsulate breast tissue without spillage at the top or sides. If there is wrinkling or empty space, you may need a smaller cup or a different cup shape.
Strap Fit
Straps should sit comfortably without digging in. They support, but most support should come from the band.
Frequently Asked Questions
Is this calculator US or UK sizing?
This tool provides a general cup progression common in US/UK-style labeling. Different brands may label DD/E/F slightly differently.
Can cup size change if band size changes?
Yes. Cup letters are relative to band size. A 32D and 36D do not have the same cup volume.
How often should I re-measure?
Every 6–12 months, or sooner if your body changes significantly.
Final Thoughts
Learning how to measure cup size gives you a strong starting point for comfort, support, and confidence. Use the calculator above, then test a few nearby sizes to find your best fit. A well-fitting bra can improve posture, reduce discomfort, and make everyday clothing fit better.