Sister Sizes
Bra Sister Size Calculator
Sister sizes use a similar cup volume with a different band and cup letter. They can help when the cups fit but the band does not - but they do not create an identical fit.
Find your sister sizes
Enter a size you currently wear to see the nearest sizes with a similar cup volume.
Your closest sister sizes
Start with the closest sister size, not the furthest size in the row. Each step changes band tension, strap position, wire geometry and how the cup volume is distributed.
When sister sizing is useful
- The cups fit, but the band feels too loose.
- The cups fit, but the band feels slightly tight.
- Your measurements sit between two band sizes.
- A style has an unusually firm or flexible band compared to what you're used to.
- Your usual label is unavailable in that style.
When sister sizing will not fix the problem
- The cups also overflow or gape - that's a cup-volume issue, not a band one.
- The wires sit on breast tissue rather than around it.
- The centre panel floats away from the breastbone.
- The cup itself is too shallow or too projected for your shape.
- You'd need to move more than one band step to get a comfortable band.
- You're only considering a sister size because your preferred size is sold out.
Why the cup letter changes
32DD → 34D → 36C
A cup letter describes a relationship to the band, not a fixed object size - moving one band step changes what letter carries the same approximate volume.
Choose the direction from the band problem
| What you feel | Try first |
|---|---|
| Band rides up; cups otherwise fit | One band down, one cup up |
| Band feels slightly tight; cups otherwise fit | One band up, one cup down |
| Both band and cups feel wrong | Recalculate, or use the Fit Checker |
| Only one style feels wrong | Try another construction before changing your baseline size |