How Sister Sizes Work
When you go DOWN one band size, you go UP one cup letter to keep the same cup volume. Going UP one band means going DOWN one cup. So 32D, 34C, and 30DD all hold the same volume of breast tissue — just on different rib-cage frames.
When to Use Sister Sizes
- Your usual size is sold out — try the sister-size up or down.
- A brand runs small or large — sister-size in the opposite direction.
- The band feels right but cups gap — sister-size down (smaller band, bigger cup).
- The cups fit but the band feels tight — sister-size up (bigger band, smaller cup).
Sister Size Chart Examples
| Your size | Sister up | Sister down |
|---|---|---|
| 32B | 34A | 30C |
| 32C | 34B | 30D |
| 34C | 36B | 32D |
| 34D | 36C | 32DD |
| 36D | 38C | 34DD |
| 34DD | 36D | 32DDD |