Measurements for a 40C Bra
To wear a 40C bra comfortably, your body measurements should fall in this range:
| Measurement | Inches | Centimetres |
|---|---|---|
| Under-bust (band) | 39.5 – 40.5 | 100 – 103 |
| Bust (full) | 42.5 – 43.5 | 108 – 110 |
| Cup volume | ~3 in difference (C cup) | |
40C 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.
- 42B — sister size up: the band is two inches larger and the cup letter drops one. Try this if your 40C band feels too tight.
- 38D — sister size down: the band is two inches smaller and the cup letter goes up. Try this if your 40C band rides up the back.
40C International Size Conversions
| Country | Band | Cup | Full size |
|---|---|---|---|
| 🇺🇸 United States | 40 | C | 40C |
| 🇬🇧 United Kingdom | 40 | C | 40C |
| 🇪🇺 European Union | 100 | C | 100C |
| 🇮🇳 India | 40 | C | 40C |
| 🇯🇵 Japan | 100 | C | 100C |
How a 40C Bra Should Fit
The most common fit issues for 40C are an over-stretched band and cups that gap or overflow. Use this five-point check every time you try on a new 40C 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 40C
40C 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 40C Bras
- Cup gaps at the top: the cup is too big — sister-size to 38D.
- Spillage over the cup: the cup is too small — sister-size to 42B or up one cup at the same band.
- Band rides up the back: the band is too loose — go down to 38-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.