Bra Sister Sizing: The Fit That Just Gets You 

 

Sister Sizing. Ever heard of it? Maybe you’re already well acquainted and swear by it every day. Or maybe you know it in some super vague context distantly related to finding a bra. Chances are, it’s likely the latter—but trust us, you’re not alone. To clear up what it means once and for all (and, more importantly, what it could mean for you) we’re here to fill you in.    

What Does a Good Fit Feel Like?    

First, let’s talk about how your bra should fit. When it’s the right size, your bra will be snug, secure, and smooth. You have three areas to check: 

• Band: This should fit snugly around your rib cage without being uncomfortably tight. Be sure that the back is straight across—did you know it supplies 80% of your bra’s support? 

• Straps: There for added security, they should stay in place without digging into or falling off your shoulders. 

• Cups: These should hold your shape smoothly without overflowing or gapping.  

  • (Pro tip: There really is a right way to put on your bra for the ideal cup fit—it’s all in the “scoop.” Your underwire should surround your breast tissue. Simply slide your hand beneath each breast and gently scoop, or lift, so that the wire isn’t resting on top of tissue itself. If your wire still sits away from your body, it’s time to try a larger cup.)

What Exactly is a Bra Sister Size? 

It’s an alternative size in which cup volume, or capacity, stays the same, while band size and cup letter change. It ensures that you’re wearing the correct band once you know your correct cup. Since you may prefer things looser or tighter, sister sizing will help you find your truest size, all in the name of having that ideal fit (re: above). 

How Does Bra Sister Sizing Work?  

In general, bra sizing is about proportions and understanding a system of sizes. Each represents a match-up of a cup volume (a letter) with a band length (a two-digit even number). 

Let’s say you currently wear a 38C. In this case, your cup volume, when combined with a 38 band, goes by the letter name “C.” That very same volume—your current cup fit—changes its name when matched with a different sized band. Because the cup volume is still the same from one band size to the next, the resulting bras are considered “sisters.” Here’s an example: 

• Sister Sizing Down: Choose one band size lower and one cup letter higher than your current bra. In this case, 38C becomes 36D. This tightens your band while maintaining cup volume. 

• Sister Sizing Up: Choose one band size higher and one cup letter lower than your current bra. In this case, 38C becomes 40B. This loosens your band while maintaining cup volume.  

When Should I Wear My Bra Sister Size?  

When your cups fit perfectly, but your band does not, your current bra’s “sister” is the likely solution. To find your sister size, keep hook setting in mind:  

If your band is too loose on the tightest set of hooks, but your cups fit, you can go down one band size and up one cup letter.   

If your band is too tight on the loosest sets of hooks, but your cups fit, you can go up one band size and down one cup letter. 

We recommend using the middle set of hooks—they provide most flexibility of fit, allowing you to loosen or tighten as you please. Just be sure to choose the setting that feels most comfortably snug.  

Your Bra, Your Choice  

The bra you wear should feel great on your body—and only you know what that means. Ultimately, you need to do what keeps you most comfortable and confident, whether that’s trying out your sister size or sticking to what you know. In any case, we’re just here for support. Happy bra shopping!