How to Measure Your Bra Size (Including Bra Size Chart)

There are different parts and design elements that go into making a bra.

Like many, you may be wondering how to measure your bra size at home. 80% of women are wearing the wrong bra size, but a lot of that has to do with the understanding of bra size and measurement remaining a mystery which is completely unnecessary. We are leveraging our bra expertise to break this all down so you never have to settle for an ill-fitting bra. Our measuring instructions will make it easy for you to find your perfect fit. A visit to our Fitting Room, our advanced online size calculator, can also make sure you find your perfect bra size.


Bra Fitting Room Quiz


Traditional Bra Sizes Explained

Bra measurements are calculated based on your band size (number) and cup (letter). This is usually determined by measuring around your rib cage, right below your breasts, and your bust at the fullest part of your chest. One item that is often overlooked, and is of the utmost importance, is your breast shape, as it plays a huge factor in your size and what type of bra will be the perfect fit for you.

It’s also important to remember that when you are looking at these measurements to not round to a whole number. ThirdLove makes bras in half-cup sizes so that you don’t have to settle for even a half an inch of discomfort — perfect for those in-betweeners!


How to Measure Your Band Size

To measure your bra band size, you will need to grab a soft measuring tape and wear a non-padded bra. Using your tape measure, stand up and measure your ribcage, right under your bust where your bra band sits. Make sure that the measuring tape is parallel with the ground and that you’ve exhaled to get the smallest measurement. The tape should be snug and tight, but not uncomfortable. Make a note of how many inches your under-bust is.

If your under-bust measurement is even, add 2 inches. If your measurement is odd, add 3 inches. This is your band size. For example, if your under-bust measurement is 32, your band size is 34. If your under-bust measurement is 33, your band size is 36. We add 2 or 3 inches to the measurement to overcome the size difference between when the elastic in the bra band is stretched or relaxed. The bands measure smaller when laid flat on a table versus when a person a wearing it, so adding a couple inches helps give you a more accurate band size.


How to Measure Your Cup Size

To measure your cup size, stand straight with your arms at your side and measure loosely around the fullest part of your bust. This is typically where the nipple is. Make sure the measuring tape is parallel to the ground and not lower or higher in one area. Make a note of your bust size.

To get your cup size, subtract your band size from your bust. The remaining number is the over-bust differential and it determines your cup size. If the over-bust differential is 0, we consider this to be an AA cup. For each inch of over-bust differential, you should go up a cup size. So, 0 is AA cup, 1 is A cup, 2 is B cup, 3 is C cup, 4 is D cup, and so forth. At ThirdLove, we also offer half cup sizes, so if your over-bust differential is 3.5, you don’t need to settle and can get a perfect fitting C½ cup!


The Importance of Knowing Your Sister Size

Your breast shape, band and cup size rarely fit neatly into a single letter and number. For example, a DD cup size is equivalent to an E cup while a DDD cup size translates to an F cup — but the cup volume depends on the band size. This is where your sister size, or bra size equivalent, comes in which can help you find a better fitting bra.

Sister sizing is when you have the same cup volume and different band size. For instance, if you find that a 34C fits great in the cups, but the band is too tight, you’d need to adjust both your band and cup size to a 36B. Remember: Any time you go up a band size, you need to go down a cup size, and vice versa. Use our helpful Bra Size Chart as a sizing guide.



How to Find Your Bra Size

Women’s breast size can change six times over the course of their lives whether it’s due to pregnancy, weight changes, or other factors. Be sure to always check in to make sure you’re still getting a proper fit and not wearing the wrong bra size.

Here are three easy steps to finding the right bra:

1. Identify Your Breast Shape

Using our Breast Shape Dictionary, see which category best describes your unique shape.

2. Be Honest About Any Fit Issues You Are Having

Identifying common problems, like gaping cups and slipping straps, can determine which size bra you should actually be wearing and whether you need to go up or down a size (or half-cup size).

3. Find Your Favorite Cup Type

Different types of bras fit women differently, and are more suited for your lifestyle. Some women prefer a wireless bra while others need more coverage. Some hunt for the perfect T-shirt bra while others feel better in a balconette. Make sure you take the time to consider which style fits you, your life, and your style the best when bra shopping.


Bra Size Calculator

Let us talk about bra size calculators. I am sure you have seen them, the websites and the apps that promise to decipher the perfect fit formula just based on your measurements. All you need to do is enter your underbust and bust measurements, and voila, in just seconds, they reveal your bra size. Sounds easy, right? Well, not so fast.

Sure, the idea seems grand, except for a few problems that lead to inaccuracy. They assume that all breasts are the same shape and that breast tissues are distributed evenly. Here's the truth, we know that breasts come in different shapes and sizes (and they are all beautiful); in fact, they have personalities of their own.

With years of experience, we understand there's more to your bra fitting experience than a number and a letter. It is why we do not recommend bra-size calculators that just use measurements. We've got the scoop on a more tailored approach to measuring bra size at home, the better solution to the "How to calculate your bra size?" question. Say hello to our Fitting Room Quiz - the virtual assistant that gets it right and makes it easy every time.

Our Fitting Room Quiz does not solely rely on numbers; we consider your breast shape and how that affects your fit, your current bra fit issues (we've all been there), and your comfort preferences. Think of it as a heart-to-heart with your trusted bra expert. With the use of actual human knowledge and our proprietary algorithm, you can rest assured of personalized recommendations for bras that are a perfect fit suiting your style and needs.


Bra Sizing FAQ's

Let's explore answers to some of the most common questions that we receive about bras!


How will you know when you have found the perfect bra size?

Oh, you'll know when it happens! It's like falling in love. When you nail the perfect size, your bra will feel comfortable and supportive; your girls will feel snug yet free—no discomfort, no pain, no irritation, just pure delight. The straps won't dig into your shoulders or slip; the band won't be riding up or sliding down. It will be a beautiful bra harmony that will leave you feeling confident and beautiful.


Does the bra style matter?

Absolutely! First for your breast shape, then for the occasion. For example, if you have shallow breasts, you may want to rock a demi or balconette bra for extra oomph. Feeling sassy? A lace bralette can suit the vibe.


24/7® Classic T-Shirt Bra



What matters most when finding your perfect bra size?

First things first, your comfort reigns supreme; more than the numbers and letters, your fit and support matter most. It might depend on knowing how to measure your bra size; that is why we have the Fitting Room Quiz.

Does Wearing the right bra make a difference?

Absolutely, all the difference! Whether you end up with sagging or quad-boobing breasts or you will enjoy a comfortable fit and support depends on it. It is not only a matter of fashion but also a matter of self-care.


Still searching for your perfect fit or want help measuring your bra size? Our Fitting Room is an advanced size calculator that has helped millions of women find their perfect size, and you could be next.