Five minutes, then stop
Sister Sizes in Bras
Same cup volume, different band. 34C, 32D, and 36B are a family. They are not identical on your ribcage.
Updated 27 Aug 2026 · 6 min read · sister sizes in bras
The grid, not a rumour
Cup volume is roughly constant along a diagonal: 30E, 32DD, 34D, 36C, 38B (UK letters — US brands mix DD/DDD). When a 34D band floats, try 32DD before you ‘size down’ into a 34C that will spill.
Shape still changes. A 32 band pulls the cups narrower and deeper. A 36 band makes them shallower and wider. Same volume, different container.
When to sister, when not to
Yes: this brand’s 34 is a 36 in real life, cups good. Yes: you are between bands and the smaller band on the loosest hook is the plan. No: the cup is the wrong shape (gaping at the top because the cut is shallow). No: you just want the band ‘comfy’ like a T-shirt — that ride-up is the tell.
| If 34C… | Sister |
|---|---|
| Band rides up, cups OK | 32D |
| Band digs, cups OK | 36B |
| Band OK, spill | 34D (not a sister — more volume) |
| Band OK, wrinkle | 34B (less volume) |
Shopping without a fitter
Order two sisters when a site has free returns. Wear the new band on the loosest hook so you have room to tighten over 6–8 months. Sports bras sister too, but compression styles care more about the band — sports fit. $35–$70 for a daily bra you will actually replace.
Questions, answered
- Is 32D smaller than 34C?
- The band is smaller. The cup volume is in the same family. Neither is a moral size.
- US vs UK letters?
- They diverge after D. Check the brand’s chart. A UK 32E is not a US 32E.
- Can I sister a strapless?
- You can. Strapless often wants a firmer, closer band — sister down in band if the cups are already right.
