When we go shopping for running shoes, we expect to be measured and analyzed and have the ability to take a few models for a quick spin on a treadmill. In fact, we appreciate it because a running shoe with a dialed-in fit makes our feet sing.

For women, the same holds true for a running bra with a perfect fit—a firm hold, with no chafing or gaping, and fabric that feels good against our skin are a few of the ideals. But unfortunately, be it from our own discomfort with the process or not realizing the importance, sports bra shopping is often reduced to guessing at sizes and settling for a “good enough” fit.

It’s time to show yourself—and your girls—some love, because “good enough” isn’t enough. And if not for you, do it because you can: Did you know the first sports bra ever made was simply two jock straps stitched together? Believe it or not, that counted as an improvement over prior options! Beyond the ick factor, that just doesn’t sound comfortable, functional or fun. But hey, we’ve come a long way, baby! Not only is there a dizzying array of style, fabric and color options, sports bras offer the support you need for your specific size and activity.

Finding the proper fit is critical. Take the time to be measured and fit, ideally at a running store, or partner with a friend, and you two can size each other. Although it may sound like an added burden, taking this essential step will save you hassle, discomfort and money over the long run.

Know Your Numbers

To find a properly fitting sports bra, you’ll need three key measurements: your bottom band, your bust and your cup size. From there, you’ll still have some trial and error that comes with the try-on process, but if you know your accurate measurements before you go into your local running store or sports shop you’ll have a much easier time of finding a few sizes to consider. Keep in mind that all brands will fit a bit differently even if they’re labeled the same size, but at least you can get a good benchmark size for a starting point.

1. Bottom Band Measurement

The bottom band number is your rib cage measurement in inches (the bottom band accounts for the majority of a bra’s support, so be sure to make the tape snug, but not so tight that it’s hard to breathe) plus four inches for an even measurement and five inches for an odd measurement. To get this measurement, place the measuring tape around your rib cage just below your breasts right about where the bottom band of a sports bra would be. For example, if your rib cage measures 30 inches, your bottom band size is 34. And if your rib cage measures 31 inches, your bottom band size is 36.

Fit Tip
Get measured while wearing a traditional lingerie bra. Sports bras are meant to compress, meaning that being measured while wearing one could affect the measurement.

2. Bust Measurement

The second number you need is your bust measurement in inches. For this, measure from your back, across the fullest part of the bust. The tape measure does not need to be as snug for this measurement.

Measuring Tip
If you don’t have a soft measuring tape, wrap a string/thread/piece of yarn around your rib cage. Mark the spot where the ends overlap, straighten it out and measure against a yardstick.

3. Cup Size

Cup size equals bust measurement minus bottom band measurement. Once you have a number, reference the chart below to determine your exact cup size. For example, a difference of five inches means you should start with a B cup.

Fit Tip
If you have extra space in the cup or if you have “spillage,” it means you should try a different cup size. Go up or down a size as needed and also consider trying a different band size. Remember, your number and cup size are a starting point and your size may vary from brand to brand. Plus, sizes overlap. For example, if a 34C isn’t feeling quite right, consider a 32D or 36B. Also be sure to adjust the straps and back closure for optimal fit. 

Cup Sizes
Difference of 4 inches = A cup

Difference of 5 inches = B cup

Difference of 6 inches = C cup

Difference of 7 inches = D cup

Difference of 8 inches = DD cup

Difference of 9 inches = E cup

Different of 10 inches = F cup

Difference of 11 inches = FF cup

Difference of 12 inches = G cup

VIDEO: How to Find Your Correct Sports Bra Size

Fine-Tune Your Fit

Again, much like shoes, finding a great fitting sports bra will usually involve trying several options and styles. Also, look at your size number as a starting point that may vary from brand to brand. It’s also time to be honest about your likes and dislikes. For example, do you prefer compression (often the preference for A or B cups) or encapsulation (aka the divide-and-conquer approach to supporting breasts), or perhaps a combination of both? And do you like pullover bras, ones with a clasp closure or ones that close in the front? Also, consider your activity. For running, you’ll most likely need a bra with high impact support. But if you are going to yoga or a spin class, low- or medium-impact support, respectively, may suffice.

Fit Tip
Once you know your number, it may be confusing to see bras labeled as small, medium, large and extra large. They offer more general support, which can work for smaller cup sizes for running and low- to moderate-impact activities, like yoga, lifting or a road ride for larger cup sizes. Again, it comes down to comfort. There are some great bras in this category, try a variety to see what works for you. A salesperson will be able to help match your number to a corresponding small/medium/large size as a starting point. 

There are options to fit just about every size and preference combination. Going to a run specialty store to be measured, having someone else check the fit and trying on variety of options will simplify the process.

Once you’re in the dressing room, follow these steps to ensure you have the right fit:

– Bend over and give your chest a little shake or scoop while adjusting the bra to ensure all breast tissue fits in the bra. You don’t want spillage from the side or top of the cups. Not only is it uncomfortable, it’s chafe waiting to happen.

– Run in place, do jumping jacks or hop on an in-store treadmill if it’s an option. Some movement is to be expected. Judge by how the bra and support feel to you, not necessarily the amount of movement you see in the mirror.

– Make sure nothing is poking, prodding or digging into your skin. If something is uncomfortable in the dressing room, chances are it will only get worse on a run.

– Check the three key fit checks: Cups, Straps and Bottom Band. Check cups for slippage or gapping, make sure your shoulder straps aren’t too tight or digging, and ensure your bottom band feels comfortably snug.

– Can you breathe? A new bra will feel noticeably tighter than an older one, and snug is good. But, you need to breathe!