Everything You Need to Know About Bra Sister Sizes
There’s a lot of confusion when it comes to bra sizing.
I know that when I was younger, I definitely had a hard time with this concept. Like most of you, I went to your everyday department store and picked out the bra I figured fit me the best.
However, I was constantly adjusting it. I would be pulling down the back of my bra while lifting up the front. To compensate, I tried tightening the straps super tight, which only made the bra even more uncomfortable. There wasn’t any support.
But I felt like I had no other options. I wasn’t taught this stuff.
Can anyone else relate?
The department stores only carry bras that they think are typical according to US standards. There is a very limited selection. This is one reason why so many women wear the wrong bra size. For many years, I was a 36DD because that is what they had available in stores.
This is nowhere close to my actual size.
Sister sizing is a great place to start learning what size you actually are. Here are some tips for finding out your correct bra size using sister sizing.
What Are Bra Sister Sizes?
There’s a huge misconception that all cup sizes are created equal when in reality that’s not the case.
Sister sizes are alternate bra sizes where the cup volume remains the same regardless of the band size and cup letter.
For example, a 30F and a 38C are technically the same size because the cup volume is the same.
Someone who is a 38DD has more breast volume than someone that is a 30DD. In other words, the 38DD has bigger boobs even though the cup size is the same letter.
30DD and 38DD are not equivalent sizes.
Of course, this is confusing for mostly everyone!
How Do Sister Sizes Work?
The band size affects the cup size. If you need a band size that is smaller, then the cup size will increase. Vice versa, if you need a bigger band, then the cup size will decrease.
Pretend you wear a 34DD.
If your band is loose, you will need reduce the band size, making your new band size 32. If your breasts fit in the cups beforehand (sometimes it can be difficult to tell when your band is really loose), your new cup size would be an E. Ergo, your new bra size is a 32E.
I know you are probably thinking…if I’m a DD and my band is too loose, why wouldn’t I just wear a 32DD?
Because the cups are dependant on the size of the band, the sister size of a 32DD is a 34D, not a 34DD. Therefore the cups would be too small if you were to wear a 32DD.
If you need to reduce down two band sizes then you would increase two cup sizes to become 30F and so on.
If you need to increase your band size, then you will need to decrease your cup size. One size up would be a 36D and two sizes up would be a 38C.
If you are wearing the wrong size completely, please refer to my article 5 Signs You Are Wearing the Wrong Bra Size. In my case, I was wearing a band that was two sizes too big and needed to go up three cup sizes.
Why Are Sister Sizes Important?
Sister sizes are meant to help you find your correct bra size. If you’re wearing the wrong size you can just decrease the band size and increase the cup size or vice versa to find the bra that fits your body.
I prefer using your sister size as a baseline to figure out your bra size because sometimes measuring is unreliable. Boobs are tricky to measure because everyone has different shapes and other factors.
If you gain or lose weight you will need to be readjusted. If you lose weight you’re going to have to drop a couple of band sizes. You may also have to drop a cup size if you lose fat from your breasts.
Alternately, if you gain weight you will need to go up in a band size and down in the cups. Unless you also gain weight in your breasts.
Changes in the body require multiple adaptations in the sizing because your band and bust are changing independently of each other. Whereas, if you start at one size without any body changes it’s easier to find your correct bra size from your sister size.
Because brands and styles will fit you differently, it is also helpful to know your sister sizes because you may need to go up or down a size. So say in one brand or style the bra fits perfectly in one size, but in another brand/style you may have to size up or down in either the band or the cups or both.
Misuse of Your Sister Sizes
There are plenty of reasons why you should know your sister sizes and how your sister sizes can be helpful. However, sister sizes are not meant to be worn in place of your correct size!
I sometimes hear people say, “There are out of my size, but that color is so cute! I’ll just get the next size up.”
Don’t do that. If you know your size, wear that size! That is the size you are.
One of the things that really irks me is when you go to get fitted and the bra fitter tells you that you are a size that you aren’t. This is usually done purposefully (I’m talking about you Victoria’s Secret!).
Usually, it’s a tactic for the salesperson to just make a sale. They don’t have your bra size in stock so they pretend that you’re a different size than what you are and try to squeeze you into this teenie, tiny bra that you have no chance of fitting into.
Why You Can Never Find a Sticky Bra That Fits
Because the cup size is reliant on the band size and there’s no band. So what is the actual cup size?
For example, a sticky bra that says it’s made for DD size cup. But is that cup based on a 32DD? 34DD? 36DD? As I just explained, the cup letter sizes are not the same.
I know, it’s infuriating! Why couldn’t all DD’s just be the same size? Well the short answer is because a lot of logic goes into a bra’s construction. That’s a topic for another article.
Conclusion
You will know you have found the right size because the band will fit comfortably, the cups will mold to your breasts, you will have minimal back fat, and you won’t have quadboob.
Again, you can refer to my article 5 Signs You Are Wearing the Wrong Bra Size to help determine your sister size.
Maybe the bra you try on isn’t a sizing issue and just isn’t the right style for you. You can check out my article 10 Best Bra Types for Full-Busted Women to help figure out what type would be best on your frame.
Different bra brands will also differ slightly in size and shape. Honestly, the best thing to do is to keep trying on different bras until you find the perfect one.
I know it can be exhausting and a long process, but it is so worth it in the end. Then you collect that bra in every single color and hope it doesn’t get discontinued!
XOXO,
Stephanie
P.S. What size where you wearing before your correct size? What is your real bra size?
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Hi! I’m Stephanie.
Welcome to my blog about boobs, bras, and body image.
It’s my mission to help others appreciate their bodies while giving tips on dealing with bigger breasts.
Before I lost weight in my torso and bust, I was wearing a 38B. After the weight loss I was wearing a 38A. But now the 38 (band) is too loss. I recently purchased a 36A cause that’s what the store measured me at but the band is too tight, the cup is fine. What size would you suggest?
You may need to temporarily wear a bra extender if you are in between sizes.
My issue is I am very shallow and the tissue is spread quite wide. I have worn a 36G in some brands that fit perfect, but it does vary by brand. I find often my band is too tight and the cups way too baggy/big at the ends, but when I go down by cup size they cut into my breast tissue along the outside of my ribcage. Any thoughts?
In addition to brands’ sizing being different, different bra shapes work better for different shaped breasts. If you have found luck with a particular shape, try finding other bras/brands in that shape. You may need a different size in different brands because they are not all the same. If the band is too tight, go up in the band size. You could also use a bra extender if you are in between sizes. This may also solve the cup issue or again find a style that works best with your breasts.
Hello. It’s so frustrating to find bras I gained some weight alot in my boobs . I measured myself with a measuring tape and my band was 36 and bust was 42 and right now I have a 38 DD but band feels alittle tight not sure why if it’s p.m.s swelling or what lol… So what size bra do u think I am? Thank you so much
Does the band ride up in the back? You may find luck with a bra extender if the band is slightly too tight but the next size up is too big. You will also need to adjust the cup size accordingly if you move up in the band size. 🙂
My bust is 38 and my band is 33 I was told to wear 38dd but the cup doesn’t fit well
What do you suggest
Hello! I would imagine that the cups are too small? If your bust is a 38 you should not be wearing a 38 band size. That is way too big. Also, that bra is probably doing nothing for you in terms of support.
I would suggest a 34 band size and G or H cups to start. If the cups are too small currently, you may need to have bigger cups than recommended. If the cups are too big, a smaller size like an F or FF. First, get the band right, then worry about the cups.
I hope this helps you. Have a great day!
my band is a 28 and bust is 34, wouldn’t that make me a 28f? I can’t find them anywhere in the U.S and I currently wear a 32D. the band is always riding up though. what would be a good substitution for 28F?
Hi! You would probably be a 28E/30DD if the cups fit at your current size. However, you have to remember that different bras will fit differently. I usually order all my bras online. Amazon makes the return process really easy. Or if you want to shop in-store Nordstrom and Norstrom Rack carry those sizes. There may also be a boutique where you live. I choose UK brands such as Fantasie, Freya, and Panache to name a few.
Hello! I was told I’m a36DD but the band is good cause I can adjust it if it’s to tight the cup size is ok but a little loose what would you suggest?
Your band should feel comfortable on the last set of hooks. The other hooks are there to tighten when the band starts to loosen and stretch. You may need to go down in the cups, but there are many different factors that contribute to determining your size. I recommend trying on a 36 D in different styles as a starting point. If the band is too loose, to begin with, you may need to go down in the band. In that case, stick with DD in the cups and go with 34 as the band size. I hope this helps.
I, for one, have been happy going from 40C to 42B, depending on the brand that I use. I had been told that your sister size could only apply to 2 sizes (twin sisters). But your explanation makes so more sense.