Sister size page
30B Sister Sizes
Sister sizes keep roughly similar cup volume by changing the band and cup step together.
Starting size
30B
Snugger band
Down one band step and up one cup step.
Outside MVP range
30B and its sister sizes across systems
Each sister size shown in every system this site covers, so you can carry the comparison into a UK, EU, French, or Australian chart without converting it yourself.
| Band feel | US | UK | EU | FR | AU |
|---|---|---|---|---|---|
| Your size (30B) | 30B | 30B | 65B | 80B | 8B |
| Looser band | 32A | 32A | 70A | 85A | 10A |
How to use these sister sizes
A sister size is worth trying when the cups on 30B feel close but the band does not. Because a cup letter describes a step away from its band rather than a fixed volume, moving the band and the cup letter in opposite directions keeps the cup volume roughly where it was while the band changes.
If 30B rides up at the back, compare the snugger band first. If the band is firm enough to be uncomfortable but the cups are right, compare the looser band. Move one step at a time: each step also shifts wire width and cup shape, so a size several steps away can share a volume on paper while fitting nothing like 30B.
Sister sizes are a starting point rather than a guarantee. Band tension, strap placement, and cup shape still change between sizes, and brand grading changes them again.
Keep comparing 30B
Nearby sizes
Understand sister sizes
Bras in your size
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