Understanding bra sizes can feel confusing at first glance, but decoding the chart is simple once you know what the numbers and letters represent. Here’s a clear breakdown, complete with examples and guidance on how “sister sizing” expands your fit options.
1. What Does the Number Mean? – Band Size
- Band size is the number (e.g., 32, 34, 36) and measures the circumference around your torso, just under the bust.
- It’s typically given in inches (US/UK) or centimeters (EU).
- Band size determines the support: Most of a bra’s support comes from the band, not the straps.
- If your underbust measures 31–32 inches, you likely wear a 32 band.
Example:
| Underbust Measurement | US/UK Band Size | EU Band Size |
|---|---|---|
| 29–30 in (74–76 cm) | 30 | 65 |
| 31–32 in (78–81 cm) | 32 | 70 |
2. What Does the Letter Mean? – Cup Size
- Cup size (A, B, C, D, etc.) refers to the difference between your bust and band measurements.
- Each letter represents about 1 inch in difference (in US sizing):
- Difference = Bust measurement − Band measurement
- 1 inch = A, 2 inches = B, 3 inches = C, and so on.
| Difference (inches) | Cup Size |
|---|---|
| 0 | AA |
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD/E |
| 6 | DDD/F |
Example Calculation:
- Band: 34 in
- Bust: 37 in
- Difference: 3 in → Cup C
- Bra Size: 34C
3. How the Full Size Is Written
A typical bra size looks like: 34C
- 34 = Band size (in inches)
- C = Cup size (based on bust–band difference)
4. What Is Sister Sizing?
Sister sizes are different bra sizes that have the same cup volume but slightly different band sizes. If your regular size feels too tight/loose in the band, you can try your sister size for a better fit.
How to Find Sister Sizes:
- If you go up a band size, go down a cup size.
- If you go down a band size, go up a cup size.
| Your Usual Size | Sister Size (smaller band) | Sister Size (larger band) |
|---|---|---|
| 34C | 32D | 36B |
| 36D | 34DD | 38C |
Why Try Sister Sizes?
- Bands may fit tighter or looser depending on brand or style.
- Sister sizes help you find comfort without sacrificing cup volume.
5. Visual Breakdown Example
Sample: 36D
- 36: The number (band size) is your underbust/ribcage measurement, rounded up.
- D: The letter (cup size) is how much bigger your bust is compared to your ribs.
Imagine a 36D
- A 36D’s cup holds the same volume as a 34DD (smaller band, up a cup) and a 38C (larger band, down a cup).
- If the 36D’s band feels tight, try a 38C. If it feels loose, try a 34DD.
6. Quick Reference Bra Size Chart
| US Size | UK Size | EU Size | AU Size | Example Cup Progression |
|---|---|---|---|---|
| 32B | 32B | 70B | 10B | A, B, C, D, DD, E |
| 34C | 34C | 75C | 12C | |
| 36D | 36D | 80D | 14D |
7. Takeaways
- Numbers = Band size (your underbust/ribcage circumference)
- Letters = Cup size (difference between bust and band)
- Sister Sizing helps you fine-tune your fit for comfort and support
Need to Calculate Your Own Size?
Try it yourself with our Bra Size Calculator and explore our full Bra Size Chart with conversion tables and fitting guides. If in doubt, try nearby sister sizes—they’re your best friend for a comfy, confident fit!