Bra Sizing: The Complete and Ultimate Guide

There are so many things to consider when picking out a new bra: what shape you want, how much coverage you’re comfortable with, the amount of support you need, and so much more. And that doesn’t even include choosing between classic neutrals or fun prints.

One of the most important aspects of picking out your bra, regardless of the answer to any of those questions, is picking the right bra size. So many people go years, maybe their entire adult lives, wearing the wrong bra size.

Although a few boutiques have bra fitters to measure you for a professional bra, there isn’t always the most accessibility to that kind of resource. Plus, not all shoppers want to go to the nearby malls, or those malls don’t have what they need. 

So, we’re here to step in and serve as a fitting guide. We’ll talk about everything from how the right bra will contribute to your overall health to how to go about figuring out your correct size so you can start the day confidently. 

Where Is the Perfect Bra? 

Wearing an incorrectly fitted bra can be more than just annoying; it can be painful.

Some people who wear bras experience body aches, and it turns out that the bra was the instigator the entire time, which is a true betrayal from the thing you needed support from the most.

If you’re one of those people unsure about what that size is, you’re not alone. Studies find that close to 81% of people aren’t wearing the right bra size.

Here are some ways that the wrong bra can put a damper on your day:

Breast Pain

Breast tissue pain is one of the most prevalent symptoms of wearing the wrong bra, bralette, or swimwear top. There are different factors that can cause this depending on the scenario:

For example, if you don a bra size that’s too small, it can squeeze too tight or pinch. Or on the other hand, if the bra you’re wearing is too big, your breasts won’t have the support they need. Your breasts may end up with too much wiggle room and wind up sore from all the movement. 

Certain athletes, like equestrians, are very familiar with this issue. In fact, around 40% of horseback riders experience breast pain from an ill-fitting bra

Back Pain

Another possible symptom that people can experience is back pain. This is a common complaint amongst people with larger breasts due to the extra weight their chest bears on their torsos. But, there are ways to alleviate that pain.

You guessed it: one of those ways is wearing the correct bra size. If you want proper support, you should ensure that the cup volume matches the volume of your breasts.

Shoulder, Neck, and Rib Pain

Your collection of bras can be cute and practical. However, sometimes the effort is too much on fashion over function. When bra straps are too dainty and thin for the silhouette, they can dig and pinch — ouch. Wider straps may help alleviate this by distributing weight more evenly. 

The issue of rib pain comes when someone is wearing a band size that is too small for them. Because the band doesn’t fit their back size, it will constrict the ribs. This will leave marks across your back and cause pain: a true lose/lose situation. 

Other Issues

Other issues resulting from improper bra sizing are bad posture (a coping mechanism for body aches that can become permanent), premature sagging, chafing, digging from the underwire, and more.

All of this to say, your bra affects you in more ways than you may have thought. Now that you have a better idea of why the perfect fit is important, let’s talk about how to pick the fit you need. 

How To Measure Bra Size

One thing about bra size is that they tend to differ between lingerie brands. So, to help you find the perfect fit, we’re going to walk you through measuring yourself so that you’ll never have to wear the wrong bra or go through the hassle of exchanging until you find the right one.

There are going to be a couple of things you’ll need. Make sure you have a soft measuring tape and your phone or pen and paper to record your measurements. Once you have those on hand, you’ll be one step closer to greater comfort and confidence.

Band Size

  1. The first step to measuring your bra band size is wrapping your tape measure around your ribcage. When doing this, place it just beneath your bust (where the bra band would normally wrap around you).
    1. Pro tip: Check that the tape measure is tight enough that there isn’t wiggle room. But don’t wrap it so tightly that you feel uncomfortable.
  2. Once the tape measure is snug, write down how many inches you measure and round to the nearest whole number.
  3. If you wind up with an even number, then you’ve got your band size. 
  4. If it’s an odd number, you’ll need to round it up or down. Round up if you have a leaner build around the band. Otherwise, you can round down if your build is softer around that area. That rounded number will be your band size.

Bra Cup Size

  1. First, you’ll measure your bust size by using the tape measure to record the measurement over the fullest part of your bust. When you wrap the tape measure around your body, keep it nice and level.
  2. Unlike how you measured for your band size, you’ll take a looser measurement. Breathe in and out to make sure that the tape measure isn’t too constricting.
  3. Next, you’re going to take one more band measurement. But, this time, you’re going to measure with the tape measure tucked under your arms, measuring the middle of the chest.
  4. Then, take your bust measurement and subtract your new band measurement from it.
  5. That number is going to tell you your cup size. You’ll just need a bra size chart that correlates your number with a cup size.

Check out TomboyX's sizing chart if you’re shopping with us today.

What Are the Different Styles of Bras?

One aspect of sizing for bras is that the type of bra you wear will likely affect the way it fits you. Think about it like jeans or even shoes. One size in low-rise skinny jeans may not feel as comfy as that same size for mom jeans, especially if they’re from different brands. 

Today, we’re going to walk through those details with you. After reading this, you’ll be confident wearing whatever style of bra you want, whether it’s a strapless or sports bra. You’ll know that it fits, that you’re comfortable, and that you can take on whatever comes your way.

Something to keep in mind is that the type of bra might influence which size works best. When diversifying your lingerie collection, you’ll need to test the waters with bra sizes.

A potential reason behind their conflicting tag sizes lies in the different amounts of material brands use to make the bras. For example, a demi bra could have less material than a full bra. That means they’re likely to run smaller than full bras, so you may need to go down a cup size and adjust your band size.

The degree of padding that a certain has could also potentially affect the size, too. Using a full bra as an example for comparison again, you’re going to have a different fit from your usual size when you wear a push-up bra. Some push-up bras have so much padding in them that they fill up half the cup. If you find your bust spilling out of the cups, try the next size up.

How Do You Know if Your Bra Fits Correctly?

While you’re testing out other bra sizes for other bra styles, here’s how to ensure it fits the way it should:

Band Fit

Getting your band fit correct is one of the most critical parts of your bra because the cup and wire don’t function as they’re supposed to when the band fits incorrectly. 

Test if the band fits by checking to see if it's snug when still on the last hook. You might be familiar with the way bras tend to stretch over time — taking this step makes you proactive in ensuring your bras last longer.

Another tip is to try to slip two of your fingers beneath the band on your back. You should be able to lift it about an inch or so from your body. Less than an inch means it’s too tight and vice versa with lifting it further than an inch.

Essentially, you want the bra to feel firm across your ribcage so that you can rely on some support from the band alone. If you’re relying solely on your straps to keep your bra up, then you have the wrong band size. It’s essential to keep your bust in place.

Cup Fit

Checking the fit of your cup is much easier and takes a quick glance. First, you’ll want to avoid spillage or gaping space. If you’re standing up with good posture and you find that your bust is spilling out of the cup, try a size up. Spillage can happen either at the neckline or by your underarms.

Then, you’ll want to size down if there is a gapping issue. When that’s the case, your bra can end up wrinkling in the cups.

Strap Fit

Before swapping your bra for another, check you’re using your straps correctly. If your straps aren’t in the right position, they can cause gapping or spilling in your cup. Pull your straps longer or shorter to find out if that will remedy the problem.

Some people prefer bras with adjustable straps, like the Lounge Bralette, so their armpits stay cool and comfy no matter what happens.

Bra Sister Sizes

One last thing we want to discuss before sending you on your way is your sister size. We mentioned earlier that brands could sometimes have differences in sizing. You can conquer this slight annoyance by knowing which other sizes are most likely to fit you.

Your sister size is the bra size that has the same cup volume but different band sizes. Usually, the rule is when you go up a cup size, you go down in band size. For example, your usual size might be 32C. Then, your sister sizes will be 34B and 30D. 

The Support That You Love

Now you have your complete and ultimate guide for bra sizing! We wish you the best of luck in your shopping endeavors for a perfectly-fitting bra. At TomboyX, we know that every body and everybody is totally unique.

That’s why we stock bras for every need, including bralettes, adaptable bras, compression tops, soft bras, and more. Choose an empowering silhouette in a print or color that makes you smile, from dinosaurs to the Pride rainbow to clouds to everything-else-your-heart-desires.


Only 'one in five' are wearing the right bra size: How to tell if yours is wrong, according to lingerie experts | The Independent

You've Probably Been Wearing The Wrong Bra Size For Years | HuffPost Voices

7 Perfect Bra-Fitting Tips By Lingerie Expert Cora Harrington | Healthline