How to Measure Your Bra Size

How to Measure Your Bra Size

portrait of Heidi Zak
Heidi Zak
Co-Founder & CEO

Traditional bra sizes explained and how you can find your perfect fit. 

Like many, you may be wondering how to measure your bra size. 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. A visit to our Fitting Room can also make sure you find your perfect bra size.

ThirdLove's Perfect Coverage Bra in Taupe.ThirdLove’s Perfect Coverage Bra in Taupe.


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! 

Discover our collection, expertly designed for the perfect fit, here:


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 measure bra size with ThirdLove's bra size chart.


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.

Here are three easy steps to finding your bra size:

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.  

Still searching for your perfect fit? Our Fitting Room has helped millions of women find their perfect size, and you could be next. 

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