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Sister Sizes: The Hack to Finding Your Correct Bra Size

You may have heard the term “sister size” thrown around once or twice, but what does it actually mean? If you’re scratching your head, don’t worry, you’re not alone! Turns out, we found that a lot of you had questions about what sister sizing is all about. So we thought, why not break it down? Read on to get the full scoop on how to find your perfect bra size.

Plus, you'll get a refresher course on how your bra should *actually* fit. Every body is unique, that's why our assortment includes the best bras for different body types. Now let’s get to it.

First thing’s first. A sister size is basically an alternative bra size to what you usually wear. It maintains the same cup volume as your typical size, but with a different sized band. The reason for choosing a sister size is if you want a tighter or looser fitted band. 

Ok, time to pause. So we know that the band size will change because that’s the issue we’re trying to fix. Now let’s rewind back to the cup. We mentioned that the cup will maintain the same volume as your normal cup. PSA: Same cup volume doesn’t mean same cup letter.

For example, someone who wears a 34B could also wear a 32C and a 36A depending on if they want a tighter or looser fitting band. For both alternatives, the cup volume stays the same as that of your starting size!

In summary…to keep the same volume in your cup but adjust the band size, you’ll need to either.... Go up in the cup and down in the band OR Down in the cup and up in the band.

Check out the bra size chart below to discover your sister sizes!

In short, choose your sister size if you feel good about your cup, but want the band to fit tighter or looser. The idea is to help you find the size that feels good and works with your body! Pro Tip: If you’re ever unsure about your starting size, use our bra size calculator here!

But why do BOTH the cup and band need to change? 

Good question. Think of it like this…the cup capacity of a 34B is not the same as that of a 36B. This means that the total volume in a B cup changes with your band size. So, if you like how the cup fits, you'll need to adjust the letter size when switching bands to ensure you keep that same capacity.

What if the band fits well but the cups are off?

This is the easiest fix! If the only issue is that the cups are too big or small, stick to the same band number size and then either go up or down in the letter size. 

How do I know if my bra fits correctly?

Spoiler: 80% of women are wearing the wrong size! Knowing if your bra fits is crucial for 24/7 comfy and supportive feels. For starters, focus on these bra fitting tips when figuring out if you’re wearing the correct bra size:

  1.  The Band Fit: The band does the majority of the work for your bra. It should sit firmly around your ribcage, but not too tight! The hook and eye closures should be set on the middle hook with about 1-3 inches of stretch when pulled away from the body. This will allow for natural fluctuations within the body and provide the most wear out of your styles. If the band rides up your back, it’s too large. If it feels overly tight or constrictive, it’s too small.
  2.  The Cup Fit: You might be wondering, “ Is my cup A or B? C or D?” And so on… As a rule of thumb, the cups should cradle the entire boobs from side to center. Pro Tip: Make sure you’re adjusting the breast tissue using the Swoop + Swoop method when filing the cups! There should be no pinching, gaping or spillage. After you put on your clothes, the bra should also provide a smooth silhouette.
  3.  The Center Gore: The center part of the bra between the cups should rest flat against your sternum. It shouldn’t poke or lift away from your body. PSA: Wirefree bras might not lay totally on your sternum – that’s normal!
  4.  The Straps: The straps should stay comfortably in place providing lift and support without digging into your shoulders. Make sure your straps aren't too tight by testing their flexibility. You should be able to lift them 1-2 inches off your shoulders using two fingers.
  5.  The Underwire: If your bra has an underwire, it should follow the natural curve of your breast without poking into your sides or center.

Let's do I find my bra size?

Don't sweat it! You’re only 2 minutes away from finding the perfect fit– and you can do it right at home. Check out the bra size calculator on our Fit Guide to get started!