You’re probably wearing the wrong bra size. It’s not your fault—the fashion industry, plastic surgeons, and media have given us all a skewed idea of what a bra size really means. Having a DD means your boobs are GIANT, an A means you are a bonafide member of the IBTC, and a C is a “happy medium”. While this is how 99% of us have been taught to think about bra sizes, this is not how it works. Let’s talk about what bra sizes mean, why you’re probably wearing the wrong bra size, how to find your actual size and sister size, and why wearing the wrong bra size can be an issue.
I want to preface this by saying that by the end of this article, you might be shocked, but you’re on your way to being really, really comfortable. Every time I’ve had a “bra intervention” with one of my friends, they are stunned at how something so simple can make such a big change in how they feel, look, and act. You probably don’t even recognize that you’re wearing the wrong bra size, but as soon as you’re in the right size for your body, you’ll notice the difference.
What Bra Sizes Mean
Although we’ve been taught for our entire lives that a big cup size means big boobs, this isn’t necessarily the case. Let me explain.
Basically, cup sizes are a measure of difference. The difference between your band measurement (right underneath your boobs) and your chest measurement (across the widest point) gives you some number of inches of difference. (Obligatory mention that I am an American and use imperial measurements, but all the conversions I use will be available in resources I link to).
The greater the difference between the band measurement and the chest measurement, the larger the cup sizes. Because things can’t be easy for boob-havers, cup sizes are different in different countries. I’m going to use the American version where a 1-inch difference=A cup, 2-inch difference=B cup, and so on and so forth.
Why We Are Wearing the Wrong Bra Size
For a lot of millennial women, our bra size was probably taken for the first time at a certain store that will not be named that happens to be named for a certain woman’s secret. The method used for measuring common in these stores (and similar) is responsible for A LOT of our struggles.
Generally, what these stores will have you do is take the inches measurement of your ribcage under your breasts, then add four or sometimes as many as six inches.
Do not do this.
I repeat, DO NOT do this. This “plus-four” method was dreamed up in the 1950s when the wonderfully stretchy synthetic fabrics of today didn’t exist. Since your bra generally should be tight across the ribcage, this method allowed for a bit of extra space to breathe when boob-havers were wearing silky bullet bras.
However, a bra that is made with current fabrics will stretch out. This means that if you start with a size that is already 4-6 inches bigger around your ribs, it won’t fit right. The majority of support from your bra should come from the band, so it needs to be snug. A band that is stretched out or too big for your ribcage won’t support the weight of your boobs, and all of that weight will be transferred to your straps.
If you find that your bra straps are digging in, leaving red marks on your shoulders, or causing neck/shoulder pain, this is a sign that you’re probably in the wrong band size.
This is an example of the “plus four” method of sizing—if I used this method of measurement, I’d probably end up in a US 34DD. This almost fits, but there’s a marked difference in how I look and feel with this size.
My actual bra size per the legit method from A Bra That Fits is 30H US, or 30FF UK (more on different country bra sizing here). When my friends and I talk about clothes, they’re always SHOCKED to hear my bra size—”an H? who has boobs that big?!” Really, it’s just because we have created this idea in our heads that bigger numbers=bigger boobs, rather than just representing ratios. This “traditional” method of measurement tends to overestimate band size and underestimate cup size.
A caveat– if you are buying a vintage bra, you might still want to use this plus-four method. For everything else, the measurement you take around your ribcage is going to be the band size. If you’re between numbers (ex. 33 inches), it’s probably best to try both a 32 and a 34 band size and see what fits you best.
How to Measure Bra Size (the right way)
If you want to go the easy route, take a measurement under your band and measurement across the widest part. The band measurement is the band size, and the difference in inches between the wide part-band is the cup size.
For a more in-depth version, I would highly recommend the calculator from A Bra That Fits. This will have you measure in multiple positions and places so you can ensure your bra fits when you’re moving around. While the “quick” method might get you closer to your actual size, the ABTF method is unparalleled.
A Note on Sister Size For Bras
Since you are all now aware that bra sizes do not tell us how much breast tissue is there, let’s talk about sister sizes.
Sister sizes are bras with the same amount of room for boob, but with different cup/band size combos. For example, a 32DDD has the same amount of space for breast tissue as a 34DD, a 36D, a 38C, and a 40B. This is why I can kind of fudge it with 34DD bras in big box stores. It’s “close enough” to the amount of boob room I’d find in my normal bras.
It’s likely that you’ve found a sister-size bra at one of these stores that shall not be named, and that’s probably the bra you wear. While it is not the optimal fit, it holds in most of your breast tissue.
Once you get your new-and-improved bra size, you can always try on bras in sister sizes and different brands. Sometimes, a bra in the “correct” size will fit weird, but a sister size up or down will make a world of difference. If a band runs tight in a certain brand, you might find that your sister size fits a bit better.
I occasionally buy bras in my sister size. Sometimes this works out great, sometimes it’s terrible. It’s not an exact science, but I can tell and feel the difference. Putting on a 30H versus a 34DD makes me look like I’ve lost 15 pounds, and my posture is significantly better.
Why This Matters
Other than being an impassioned advocate for having a good reason to buy fun bras, this is actually a pretty significant deal.
There’s a correlation between wearing the wrong size bra and increased thoracic pain, a poorly fitted bra can cause occupational risks (like this article which talks about breast-related discomfort and body armor for police officers), and there’s even an entire field of sports medicine research dedicated to how to improve sports bras for optimal performance.
I probably don’t need to go into depth on all the boob-related issues in the literature, as most people with boobs are probably well aware. Whether it’s related to the cup not fitting correctly or the inability to do any kind of athletic activity without feeling like the girls are flying all over the place, we’ve probably all complained about it at some point.
Getting Out of the Wrong Bra Size
Congrats, you’ve now measured your boobs and you’re on the way to feeling more comfortable!
If you find that you no longer fit in the unnamed-store’s sizes, then welcome to the club. It’s almost like people are intentionally mis-sized to ensure they fit that range…
I get nearly all of my bras online at this point. I tend to order from Bare Necessities, as they have free and fast shipping within the US, and I can order 5-6 bras and only keep the one that fits really, really well. HerRoom, Nordstrom, and Fig Leaves are other faves.
Some of my favorite bras:
Obviously, these bras are the best I’ve found for my bra size and my boob shape. Your results may vary, as different breast shapes play a role in how bras fit and how sizes may work for you. In the interest of brevity on this “that’s my TED talk” type article, I’ll link you all to this amazing Reddit wiki on breast shape, again from the geniuses at A Bra That Fits. This is only meant as an introduction to the world of happy boobs!
Otherwise, I hope you all enjoy the newfound comfort, confidence, and slightly-less-horrible adventures you will undergo with your new bras! I’ve made it my unofficial mission to get people out of the wrong bra size, so please share this with anyone you know who may be riding the boob struggle bus.
Let me know below if you’re interested in more of this type of content, or if you’d be interested in my science-y debunkings of other things we’re probably all getting wrong.
Some of the links in this article are affiliate links, meaning if you buy through them, I may receive a small commission, at no extra cost to you. Thank you for supporting my writing!