Measurements for a 30B Bra
To wear a 30B bra comfortably, your body measurements should fall in this range:
| Measurement | Inches | Centimetres |
|---|---|---|
| Under-bust (band) | 29.5 – 30.5 | 75 – 77 |
| Bust (full) | 31.5 – 32.5 | 80 – 83 |
| Cup volume | ~2 in difference (B cup) | |
30B Sister Sizes
Sister sizes share the same cup volume but use a different band measurement. They are the most useful "Plan B" when your usual size is not in stock or fits slightly off.
- 32A — sister size up: the band is two inches larger and the cup letter drops one. Try this if your 30B band feels too tight.
- 28C — sister size down: the band is two inches smaller and the cup letter goes up. Try this if your 30B band rides up the back.
30B International Size Conversions
| Country | Band | Cup | Full size |
|---|---|---|---|
| 🇺🇸 United States | 30 | B | 30B |
| 🇬🇧 United Kingdom | 30 | B | 30B |
| 🇪🇺 European Union | 75 | B | 75B |
| 🇮🇳 India | 30 | B | 30B |
| 🇯🇵 Japan | 75 | B | 75B |
How a 30B Bra Should Fit
The most common fit issues for 30B are an over-stretched band and cups that gap or overflow. Use this five-point check every time you try on a new 30B bra:
- The band sits horizontally across your back at the same height as the front.
- You can fit two fingers — but not more — flat between the band and your back.
- The centre gore (front piece between the cups) sits flat against your sternum.
- The cup encloses your breast tissue with no gap at the top and no spillage at the sides.
- The straps support the bust without digging into your shoulders.
Best Bra Brands for 30B
30B is widely stocked. Try Victoria's Secret, ThirdLove (offers half-cup sizes), Aerie, Calvin Klein, Soma, and Wacoal. For Indian shoppers, Enamor and Jockey India both fit well.
Common Issues with 30B Bras
- Cup gaps at the top: the cup is too big — sister-size to 28C.
- Spillage over the cup: the cup is too small — sister-size to 32A or up one cup at the same band.
- Band rides up the back: the band is too loose — go down to 28-band with the cup up one letter.
- Wires sit on breast tissue: the cup is too narrow — try a different brand or full-cup style.