How to Measure Sports Bra and Size


Shopping for bras is almost never an easy undertaking. It gets even more complicated when you start to shop across different brands and styles.

For the most part (although different brands do different things) sports bra sizing is similar to everyday bra sizing. However, as you read on, we’ll make it clear that relying on your own at-home measurements isn’t going to set you up for success every time.

First, though, let’s recap that standard approach to measuring bra size:

The Standard Approach to Measuring Sports Bra Right Size

Bra sizes are always made up of a number and letters, 32D, 36C, 34E and so forth… The number part is your band size and the letter indicates your cup size.

Here’s how you measure your sports bra size: First, you’ll want to strip down. Either go bare or wear an unlined/unpadded bra that keeps your natural shape (i.e. not push-up).

sports bra

First, Measure Your Bra Band Size

Use a (flexible, sewing) measuring tape to measure around your torso directly under your bust, where a bra band would sit against your rib cage.

Remember the idea is that you get most of your support from the underwire or band rather than all the support coming from your shoulders (ouch!) So, the tape should be level and snug beneath your bust and against your rib cage, parallel to the ground. The measurement in inches is your “band size”, according to this method. 

Let’s say you measured 34, add 2! Then your bra size starts with 36.

If the number you measure is odd or a fraction, round up to the nearest even number. E.g. if you measure 33 or 33.5, round up to 34, then add 2.

Then, Measure Your Bust Size

The second measurement you need to take doesn’t appear in the bra size, but it is used to calculate the cup size. 

So, now, using the same measuring tape, measure around the fullest part of your bust. If your breasts are fuller at the bottom, it may be easier to lean forward from the waist when you measure the fullest part. You’ll want to try to have the tape run parallel to where it sat when you measured your band.

Let’s say you measured 38 here.

Finally, Calculate Your Cup Size

Now, to calculate your cup size, you’ll subtract your band size from your bust size. Each inch represents a cup size, as shown from in the table below.

For our example, that’s 38 minus 36, which is 2.

2 inches is a B cup.

So the bra right size according to this method is 36B.

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Bust Size minus Band Size (inches)

Cup Sizes

<1 inch











DD / E











As you shop for bras or attend fittings, you may notice your bra size goes up and down as you shop across brands. In part this is because this traditional method isn’t really standard.

Why Measuring Yourself Isn’t Always Reliable

While there’s nothing wrong with going through the steps outlined above, it’s not a reliable method of finding your right size that we would recommend. Why? Because different brands measure differently…

If you’re shopping for a sports bra size, you may notice that many brands don’t observe the standard bra size (e.g. 36C) but have sizes ranging from 1-4, or run small, medium, large etc. which can confuse you even more.

Think of it this way: When you go jean-shopping do you find yourself able to wear the exact same size in every brand and style of jean? No, right?! Much as it sucks, there’s something to be said for trying every pair on. 

Sometimes, you can even be surprised that a style you love on the hanger, you hate in real life. Because not only are there differences across bra brands, every woman’s body is different too. That’s why we really recommend getting fitted instead of relying blindly on your own measurements. 

Good news: You don’t have to leave your house to get professionally measured at Knix!

What to Expect from a Knix Virtual Fitting:

  • Book your virtual fitting here
  • We’ll connect you with one of our expert Knix team members for a 1-on-1 fitting session over video chat. 
  • For your bra fitting, we recommend you wear a bra with little or no padding and a fitted t-shirt to ensure we get an accurate measurement. You’ll also need either a) a soft measuring tape or b) a piece of string or cord and a tape measure or ruler.
  • With different styles and sizes for 30A to 42G in the world’s most comfortable and supportive wireless bras, our fit experts can help you get into something that you will love to wear every single day.

Important Consideration: Impact Level

When you shop for sports bras you’ll sometimes notice that brands indicate “impact level” on different styles.

Impact level refers to the amount of movement (and therefore bounce) your activity entails. For example, running, jumping, dancing are considered high impact, while lifting weights is sometimes low or medium impact.

Note: Impact doesn’t reflect how good a workout you get (weightlifting is an awesome workout, you just won’t bounce around as much doing it as you do with other sports).

Here’s a handy overview of exercises x impact level:

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Impact Level

Activities Like...


Hatha yoga, walking, strength training


Hiking, cycling


Running, high intensity workouts

It’s worth noting that if you have larger breasts (greater than a C cup), you might consider wearing a high impact bra even for low to medium style activities as you probably need more support in general.

Another Important Consideration: Sports Bra Styles

Now that you’ve considered your size and impact level, it’s worth looking at the different styles of sport bras. In general, there are 3 designs:

1. Compression

Compression bras focus on doing exactly that - compressing your boobs against your chest wall, so they lie as flat as possible against your body. By compressing you, they minimize movement and bounce.

However, compression bras do not have cups built in for each breast and can also cause an appearance of “uni-boob”. Many women won’t be bothered by this, but others will want to preserve their breast shape even when working out.

2. Encapsulation

Encapsulation bras do have cups that surround and shape each breast. There is generally no compression with these bras, which makes them ideal for low impact activities.

Because each breast is “cupped”, encapsulation bras do a good job preserving your natural body shape.

3. Encapsulation-Compression

Don’t want to choose? You don’t have to. There are bras that do both! These bras usually have an inner layer that provides cupped support and an outer layer or band of material that compresses your boobs against the chest wall.

These bras provide the best-of-both-worlds in terms of both appearance and support and can be good for high impact levels of exercise and all sizes of chest.

Other Sports Bra Features to Consider

In addition to compression or encapsulation as types of bras, there are other features that provide more options for you. Depending on your size, style and exercise impact level, some of these features may be more important than others.

  • Adjustable straps: Adjustable straps allow you to lengthen or shorten straps depending on your torso size and shape. For larger bust sizes (C cup and above), adjustable straps are more important as more support is required.
  • Strap style: As sports bras have become more fashion-forward (and are often worn revealed, or even without tops), different styles of straps have emerged. There’s the traditional tank top style (often a pullover bra). There are also racerback—if you experience slipping shoulder straps a lot, you may love this style. There are also crisscross straps that make a bigger style statement.
  • Underwire: As with regular bras, sports bras come with and without underwire. While underwire is often considered to offer more support, it can also be uncomfortable for many women. Underwire bras are also more likely to require handwashing. With many technical fabrics and designs on the market, underwire is a personal choice rather than a support necessity.

How to Evaluate the Fit of Your Sports Bra

When you try on a sports bra, you’re looking for slightly different things than when you shop for a regular everyday bra. Here are some of the things to really look for:

  • Support: Obviously support is the point of all bras, but really test it with a sports bra. Do a few jumping jacks and make sure you feel supported and confident. Your sports bra should be smooth across your bust and back. Wrinkles are a sign that there’s excess fabric, so try sizing down.
  • Coverage: While there are “sexy” sports bras that show cleavage, most of the performance-focused sports bras give you full coverage. There should be no cleavage or spillage with these sports bras. You should be fully and comfortably contained with no bulging above the cups or at the back.
  • Comfort: Even if you’re not quite Serena Williams, you want to focus on your performance, not your bra. So you want a bra that doesn’t distract you. If straps dig in or feel too constrictive, or if the band is too tight on your rib cage, it may become painful and/or distracting once you hit the gym or field. Although sports bras always feel a little constrictive, they should never be painful or uncomfortable.

Caring for & Replacing Your Sports Bra

Once you have found the perfect sports bra, you’ll want to care for it properly. 

  • Wash your sports bras regularly: We wrote a whole other article about washing your sports bras. But the general rule of thumb is that they require much more frequent washing than your everyday bras. This is because sweat can really break down the fabric.
  • Keep a few sports bras in rotation: Because sports bras get warm and damp, they need time to “relax” back to their original shape between washes and workouts. So keep a few in rotation and you’ll always have a clean and supportive bra.
  • Look for signs that you need to replace your bra: A sports bra will last a year, or about 40 washes maximum. But don’t ignore signs that it’s time to replace. Those signs include: Damaged hooks, fabric pilling, elastic showing visible breakages, a general sense that the bra is no longer supportive (loosened steps etc.) 

And remember when it’s time to replace your sports bra, it’s a great opportunity to get fitted again and make sure you’re still in the best size and style for your body!