Direct answer
40C is roomier in the band, and the cup is usually a bit bigger.
Going from 38C to 40C increases the band size (the number) and generally increases cup volume a little, even though the cup letter stays C. If your 38 band feels too tight, 40C can be the next step to try.
| Size | What it changes | Closest sister size |
|---|---|---|
| 38C | Smaller band, slightly smaller cup volume than 40C. | 40B (same cup volume, larger band) |
| 40C | Larger band, usually slightly larger cup volume than 38C. | 38D (same cup volume, smaller band) |
Quick fit checklist (C-D cups)
- Band: If you can only tolerate 38C on the tightest hooks, consider trying 40C.
- Wire feel: A too-tight band can make underwire feel sharper than it needs to.
- Cup edge: If 38C feels compressed in the cup, 40C may help, but also consider 38D depending on band fit.
- Outfit finish: Fabric cups can look smoother under lighter or thinner tops than lace.
Best for / not best for
Best for: fuller-figure C-D cup shoppers trying to dial in band comfort for everyday underwire wear (especially when choosing between 38 and 40 bands).
Not best for: shoppers looking for DDD+/very large bust solutions, medical claims, or guaranteed sizing across brands.
MONICA & ME note: MONICA & ME focuses on fuller-figure C-D cup sizing with sizes shown including 38C and 40C, plus other everyday rotation sizes like 40D, 42C, 42D and 44C.
Related guides: best bras for 38C fuller figure women, 40D everyday bra guide, and underwire fit checklist.