On top of being highly technical garments, bras are also complicated in the way their sizing works. For example, a woman who wears a 32G cup isn’t necessarily a true G cup. Confusing, right? But stay with us — we’ll explain how bra sizes work in just a bit. It’s no wonder that 80 percent of women are wearing the wrong size when one’s cup letter doesn’t directly translate to their cup volume. See why your measured bra size may not be your actual bra size.
First things first, let’s talk about sizing a bra the traditional way. Bra size measurements are calculated based on your band size (number) and cup size (letter), which are typically determined by using a tape measure around your rib cage and bust. If you’d rather skip the dressing room, ThirdLove offers an online Fitting Room Quiz that matches you with your bra size and recommended style based on your unique breast shape. Regardless of what method you choose, you’re left with a number and letter that is your bra size.
There are a few things to check when trying on a new bra to determine whether it fits you well:
Find more information on how a bra should fit on our website.
While understanding bra sizes is a great starting point, it is important to remember that the perfect fit goes beyond the band sizes and cup sizes. Yes, that 34C might technically be your "size," but if it's leaving you fidgeting all day, it's time to re-evaluate. A well-fitting bra should not only be the correct size but also comfortable, supportive, and flattering. Why? Because every brand, style, and even fabric can slightly change how a bra fits.
Bra sizes can vary significantly between different manufacturers. Equally, you might find that in some bra styles, you need to go a cup size up for added coverage, while others work with your usual size. It's all about the design and fit. Don't be shy about experimenting with different cup sizes and styles to find your comfort zone. In the end, your true size is the one that feels best, not the one printed on the tag.
Additionally, different activities can demand different fit requirements. A sports bra, for instance, is designed to provide maximum support during high-impact workouts and might, therefore, be tighter than your regular bra.
Now, here’s where things can get a little tricky. For reference, any cup with a 34 band size is considered a “true cup” size. This means that a 34AA is in fact a AA cup, just as how a 34B is a true B cup. However, a 34B is also equivalent in cup volume to a 30D, 32C, and a 36A. All three aforementioned sizes are a B cup despite what their cup letter indicates. This is called sister sizes.
Take a look at our bra size chart below for reference. All bra sizes in the same row across share the same sister size, aka they’re all equal in cup volume. Let’s do another bra cup size comparison: if you wear a 32D, you are actually a true C cup. An easy way to determine your true cup size is simply to locate your bra size on the chart below and see which cup letter is paired with a 34 band in your row.
Knowing your sister size can be helpful when adjusting your bra size. For example, if the cups fit comfortably, but the current band size is too loose, you’ll have to try a smaller band size as well as a larger cup size to maintain the same cup volume. So if you were in a 36F, going down in the band size alone would result in a cup size too small. Though the 34F sounds like it has the same cup volume as the 36F, it’s actually one cup size smaller. To keep the cup volume the same, you’ll need to try a 34G, which ensures a snug and comfortable fit, while maintaining the same cup volume as the 36F.
There are a few things to check when trying on a new bra to determine whether it fits you well:
Find more information on how a bra should fit on our website.
Many women struggle to find a good-fitting bra. Watch out for these common fit issues when bra shopping:
So, how do bra sizes work for different types of bras?
There are two primary ways of sizing bras depending on type. The first is standard bra sizing, which indicates the band size (a numeral) and the cup size (a letter). Some breast or bra size examples you might see according to this sizing method include 34A, 38B, and so on. This is the way that most bra types and styles are sized, making it essential to familiarize yourself with your own traditional bra size and its sister sizes. At ThirdLove, our bras come in a huge range of band and cup sizes, even including half cups so you can find your perfect fit!
The other way to size bras is more simplified. Certain types of bras, such as sports bras and bralettes, come in sizes XXS through XXL instead of in specific band-cup size ranges. These bras tend to be less structured, making this simpler range of sizes realistic. At ThirdLove, we recognize that there are a lot of people looking for wireless bralettes, bras, and sports bras that still require good support to feel comfortable. That's why we created wireless bras with Precise Sizing™, offering 3x more sizes than other wireless bras to account for larger and smaller cups. Our wireless bras will provide amazing support for up to G cups!
Similarly, we know how awful sports bras can be. We found that most were either comfortable but unsupportive, or supportive but restricting and uncomfortable. That's why we designed a better sports bra! Our Kinetic Adjustable Sports Bra comes in your regular bra sizing to provide you with the best support and comfort possible, regardless of your size!
It's recommended to measure your bra size every six months to a year or if you experience significant weight changes, pregnancy, or menopause.
Different brands may use slightly different sizing standards or have unique models, leading to size variations.
Bra sizes have two components: a band size, which is a number, and a cup size, which is a letter. The band size is the measurement around your underbust in inches. The difference between your bust measurement and your underbust determines the cup size.
These often use S, M, and L sizing. Check the brand's size chart, which usually correlates their letter sizes with bra sizes.
There is a lot to think about when looking for the perfect bra! At ThirdLove, we offer a variety of bras in a wide range of sizes, even including half cups, to suit every shape and size. If you’re still not following along (you’re not alone!), you can always take our quick online Fitting Room Quiz to figure out your perfect fit.
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Returns & exchanges free for 60 days for all orders. Please try on the bra to ensure a good fit, making sure to leave the original tags attached. We only accept underwear in unworn condition, with original tags, in its unopened original polybag. Items marked final sale are not eligible for return or exchange. If something’s not right, we can help. Our Fit Experts are available via live chat, or email to answer any questions you might have.
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Styles in AA-H, including half cups
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