What is a Sister Size?
Have you heard of this — your bra’s “sister size”? What is a “sister size” anyway?
Simply put, a sister size is a bra size that has the same cup volume as your bra size but a different band length. So the cup holds the same amount of breast tissue, but the measurement around your body is different.
You will have two sister sizes.
Not sure why, but Cinderella’s two step sisters just came to mind…. Sorry, I digress.
One sister size will go DOWN a band size and UP a cup size from your correct size. The other sister size will go UP a band size and DOWN a cup size from your size.
The reason why people think this works is because all those three sizes have the same cup volume. Notice in the graphic that the breast size is the same, but the width around the rib cage is different, as is the space between the breasts.
Ladies, I am here to tell you — be cautious of buying a sister size bra. It is not the same as wearing the size that fits you.
Some salespeople will try to sell you your “sister size” if your size is not available. The salespeople will say it’s a perfectly normal thing to do. That everything will be okay.
Well it’s not. It’s not okay to put you in the wrong size bra.
There’s a lot more going on with the bra fit than just the cup size.
Think of a 36 C cup, and then think of a 40 C cup. You will notice that a 36 C cup looks much different than a 40 C cup. That is because the 40 C cup contains more breast tissue. Yes it’s the same cup letter, but the width around the body of a 40 C cup is 4 inches greater than a 36 C cup.
Here’s the chart from my last post: How to Measure Yourself for a Bra. Each letter cup size represents 1 inch of projection of breast tissue from the chest.
So if you have a 40 C cup, your breast tissue will project 3 inches from your chest wall. Likewise, if you have a 36 C cup, your breasts will also project 3 inches forward. However, the 40 band has a larger girth, therefore, it takes a lot more breast tissue, covering a larger area, to project 3 inches.
When the band size changes, other things change as well, even with the same cup volume, as with the sister size. These are the areas that you may find problematic if you go with a sister size.
- Strap placement
- Bridge width
- Under arm area
The sales people forget to tell you about those things. Or maybe they just don’t know.
So instead, they just tell you to put your hooks on the last row of eyes if you’re going down a band size (a 34 C going down to a 32 D). Or they will tell you to put your hooks on the first row of eyes if you’re going up a band size (a 34 C going up to a 36 B).
What they don’t tell you is that if you go down a size, your straps will be closer in, not to mention the band will be too tight. Yes, it will eventually stretch as the elastics give over time, but that doesn’t change the fact that the band you are wearing was designed for a body more narrow than yours.
Also, if you go up a size, the opposite is true. Your straps will be too close to the edge of your shoulders, and you may have problems with them slipping.
Once the elastics start to stretch on the bigger band size, you’re out of luck because if they are already hooked on the first row of eyes, you can’t go any tighter. And when that band starts riding up in the back, forget about it. You just lost the majority of your support!
As if those reasons weren’t enough to stay away from the sister sizes, you may also have problems with the band under the arm. If you’ve ever worn a bra where the band goes just under the arm pit, then you know how uncomfortable that can be.
So you see, it’s not the same thing. Sister sizes may have the same cup volume, but that’s it.
And that, my friends, is the truth about sister sizes.
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