Ever struggled to find your bra size in stock? Or maybe your usual size feels too tight or too loose? That’s where sister sizes come in—an easy way to expand your bra options while keeping the same cup volume.
What Are Sister Sizes?
Your bra size is a combination of band size (rib cage measurement) and cup size (breast volume). But did you know that cup sizes aren’t fixed? A DD cup on a 28 band is much smaller in volume than a DD on a 40 band. That’s why understanding sister sizes is so helpful!
Sister sizing means adjusting your band and cup size while keeping the same breast volume. Here’s how it works:
Need a larger band? Go up a band size and down a cup size. (e.g., 34C → 36B)
Need a smaller band? Go down a band size and up a cup size. (e.g., 34C → 32D)
Why Sister Sizes Matter
More Bra Options – If your usual size is hard to find, sister sizing gives you alternatives.
Better Comfort – Perfect for fluctuating weight, bloating, or pregnancy.
Improved Fit – Helps with unique rib cage shapes or sensitive skin.
The Limits of Sister Sizing
Sister sizing works best within one or two size shifts. Beyond that, the bra’s structure changes, and you may lose support. For example, bras designed for DD+ cups often have firmer materials and stronger underwires, which you won’t get by sizing into a smaller cup range.
What This Means for You
Forget the idea that cup size alone defines your bra. A “D cup” isn’t the same across all bands—28D, 34D, and 40D are completely different! Finding the right bra may mean trying different sizes, even if you’ve worn the same one for years. And that’s okay!
At the end of the day, what matters most is how your bra feels. If the size tag bothers you, cut it out—but never settle for an uncomfortable bra. Your comfort comes first!