Sports Bra Size Guide: How to Measure and Find Your Fit
To find your sports bra size, measure around your rib cage just under your bust for the band, measure around the fullest part of your bust, and subtract the first number from the second. Each inch of difference moves you up one cup size. Then check the result against the specific brand’s chart, because sports bra sizing is not standardized, and confirm it by moving in the bra.
This guide walks through each step with a worked example, explains how to read brand charts, shows what a good fit feels like, and helps you match support level to your activity.
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TL;DR
Measure your band snugly under the bust (exhale first) and your bust at the fullest point, then subtract to get your cup.
Your sports bra size is generally your regular bra size, but alpha sizes (S, M, L) and cup ranges differ by brand, so always use the brand’s own chart.
A good band is snug, with room for no more than two fingers. The band does most of the work, not the straps.
Choose support by activity and cup size: running and jumping call for more support than yoga or walking.
Re-measure every time you buy, since weight changes, pregnancy, hormones and age all shift your size.
Table of Contents
What you need before you measure
You need a soft, flexible tape measure (the sewing kind, not a metal one), a mirror, and a few quiet minutes. Measure against bare skin if you can, or over a thin, unpadded bra. Padding, molded cups and a thick sports bra will add inches that are not yours.
Stand up straight with your arms relaxed at your sides. Keep the tape parallel to the floor at every point, which is easiest to check in a mirror. A tape that dips at the back is the most common reason people end up with a band that is too big.
If you would rather skip the tape altogether, our guides to finding your bra size at home and bra fitting measurements cover other ways to get the same numbers.
How to measure your sports bra size, step by step
Step 1: Measure your band
Wrap the tape around your rib cage, directly under your bust, where a bra band would sit. Exhale fully before you read the number, so you capture the smallest measurement. Runner’s World recommends rounding each measurement up to the nearest whole inch and, if the result is an odd number, rounding up to the next even number for your band size.
The tape should be snug but not digging in. You should be able to breathe normally and slide one finger under it.
Step 2: Measure your bust
Now wrap the tape around the fullest part of your chest, usually across the nipple line. Keep it level around your back and do not squeeze. You want the tape resting against you, not flattening you.
Step 3: Subtract to find your cup
Subtract your band measurement from your bust measurement. The difference in inches points to your cup. By the Runner’s World method, a one-inch difference is an A, two inches is a B, and so on up the alphabet.
Bust minus band Typical cup 1 inch A 2 inches B 3 inches C 4 inches D 5 inches DD (sometimes called E) 6 inches DDD (sometimes called F)
The letters past D are where brands disagree most. Some charts start the scale a cup earlier, so that a given difference lands one letter lower, and some label the cups after DD as E and F while others use DDD and DDDD. That is not a mistake in your math. It is the reason a brand’s own chart always has the final say.
A worked example
Say you measure 34 inches under the bust and 37 inches across the fullest part. Your band is 34 (already even). The difference is 3 inches, which gives you a C. Your starting point is a 34C.
Now say your underbust is 33 inches and your bust is 37. Round the band up to 34 and you get 3 inches again: still a 34C. If your underbust is 31 inches and your bust is 35, the band rounds up to 32 and the difference becomes 3 inches, so you start at a 32C.
A starting point is all this is. Measurements get you into the right neighborhood, and trying the bra on finishes the job.
Is your sports bra size the same as your regular bra size?
Usually, yes: your band and cup come from the same measurements. What changes is how a brand labels the result. Many sports bras use alpha sizes such as XS, S, M and L instead of numbers and letters, and a single alpha size often covers several cup sizes. A 34C might be a small in one brand and a medium in another. Some brands offer both systems: alpha sizes for lower-impact styles and band-and-cup sizes for higher-support ones.
So take your calculated size, open the size chart on the product page, and find the row where your band and cup both fit. If you land between two sizes, the band measurement usually matters more, because that is where most of the support comes from. If a chart lists a size range, think about what you are buying: a compression style that pulls you in suits the lower end of the range, and an encapsulation style with separate cups needs the cup to be right.
Do not size down for extra support. A smaller band than you measure will ride up, dig in, and leave you uncomfortable. Pick a style with more support instead.
What size is a 34C in a sports bra?
There is no single answer. Depending on the brand, a 34C is commonly a small or a medium in alpha sizing, and some brands group it with A to C cups in one size. Find the 34 band and the C cup on the specific chart before you order.
How a sports bra should fit
Once you have a size, try it on and run through this checklist. Our approach is to treat the numbers as a hypothesis and the try-on as the test.
The band
The band should sit snugly and level around your rib cage. You should be able to fit no more than two fingers between the band and your body. If the band rides higher in the back than in the front, it is too loose, and a smaller band is the fix. Raise your arms overhead: if the band lifts or breast tissue peeks out beneath the cups, go down a band size.
The band matters more than anything else. Wirecutter’s lingerie expert Iris Clarke explains that most support comes from a snug band rather than tightened straps, so tightening the straps to compensate for a loose band will not work and will start to hurt your shoulders.
The cups
Your breasts should sit centered and contained, without gaps at the top of the cup, wrinkles in the fabric, or tissue spilling out at the sides, neckline or underarm. Spillage means the cup is too small; gaping or wrinkling means it is too big. If you are between cups, try the other size and compare how the fabric lies.
The straps
Straps should stay in place without cutting into your shoulders. Adjust them last, after the band is right. If a strap keeps slipping, it may be too loose, or the style may not suit your shoulder shape. A racerback or a more closely set strap is worth a try.
The movement test
Before you commit, jump, jog in place, twist and swing your arms. Too much bounce, any chafing or pinching, or tissue shifting out of the cups means keep looking. Measurement gets you close, but only moving shows whether the bra works.
If your body is changing, for example during pregnancy or after birth, fit will change too. For that stage, this guide to pumping bras that fit well explains what to look for in a bra when your bust size and shape are in flux.
Sports bra support levels: low, medium and high
The right support level depends on two things: how hard you move, and how large your cups are. A runner with a small bust may still want more support than a person with a large bust who mostly stretches or walks.
Support level Best for What to expect Low Yoga, Pilates, walking, stretching Light compression, often pullover styles, thinner bands Medium Cycling, hiking, gym classes, strength training A firmer band and more shaping, with a mix of compression and separate cups High Running, HIIT, jumping, court sports Wide band, adjustable straps, and often encapsulated cups that hold each breast separately
Two practical rules help you choose:
Go up a level as your cup size goes up. Larger cups generally need more structure for the same activity.
Match the bra to your hardest workout. If you run twice a week and do yoga four times, own at least one high-support bra for the runs.
High-support bras tend to have the widest bands and adjustable straps, and they are the styles most likely to use separate cups. They also tend to take longer to put on, which is a fair trade for activities where you jump or run.
When to re-measure
Your size is not fixed. Weight changes, pregnancy, breastfeeding, hormonal shifts and aging can all change your measurements. Runner’s World advises recalculating whenever you buy rather than assuming last year’s size still applies. It takes two minutes and saves you from a bra that no longer works.
It also helps to rotate between several sports bras instead of wearing the same one every day. The elastic recovers between wears, and you get more life from each one. Replace a bra when the band stretches so that you are on the loosest hook all the time, or when it stops holding you in place.
Why sizing is so inconsistent online
Buying a sports bra online is harder than buying a T-shirt, because the margin for error is smaller. A half-inch difference in the band changes the feel entirely, and every brand cuts differently. The same 34C can feel tight in one brand and loose in the next. Returns on intimates and activewear are often limited for hygiene reasons, which makes a wrong guess more expensive.
Three habits cut the risk:
Use the brand’s own chart, every time. Do not assume your last size carries over.
Read the fit notes and reviews. Look for comments from people with your band and cup size, and notes such as “runs small in the band.”
Know your numbers. Keep your band, bust and difference written down so you can check any chart quickly. Our sportswear fit guide covers the few measurements that matter most across activewear, and the bust, waist and hip measurement guide helps if you also want to size tops and leggings.
For general principles that apply to any garment, see our online shopping size guide and our walkthrough on how to measure accurately.
Our perspective: sizing is a data problem, not a you problem
Most people who struggle with sports bras do not have unusual bodies. They have a system that gives them a different answer every time they shop. A size chart is a brand’s best guess about a typical customer, and a tape measure held by someone without a mirror, a helper or practice is a noisy tool. When the two disagree, shoppers blame themselves.
We think the fix is to work from your own body and to keep that information somewhere you can reuse it. That is why we built ClothME around a size profile you create from two photos, with no tape measure involved. The profile is saved, so you do not start from scratch with each brand. It also works for the people you shop for: you can save profiles for your partner, your teenager or your kids, so that one account covers a whole household.
For sports bras specifically, we would still say the same thing a good fitter would: use the measurements to narrow the field, check the band first, and trust how the bra feels when you move. A profile makes the narrowing faster and more consistent. It does not replace the try-on, and it does not replace the support-level decision, which depends on what you do in the bra.
— admin
Skip the guesswork with a saved size profile
If you are tired of measuring, converting and second-guessing, try our Free Size Tool. Upload two photos, get a size profile, and see products that match your size along with your style, color and fabric preferences. You can save profiles for family members too, which is useful when you are shopping for a teen who is growing out of their sports bras every few months.
A quick checklist before you order
Measure your band and bust today, not from memory.
Calculate your cup and note your band rounded to an even number.
Open the brand’s own chart and match both band and cup.
Choose the support level for your hardest activity.
Read reviews for fit notes from people at your size.
Check the return policy before you buy.
On arrival, test the band, cups and straps, then jump and twist.
FAQ
How do you know what size sports bra to get?
Measure under your bust for the band and across the fullest part of your bust, then subtract the band from the bust to get your cup. Match both numbers to the brand’s size chart, since each brand sizes a little differently. Then try it on: the band should be snug, the cups smooth, and nothing should bounce when you jump.
Is a sports bra size the same as a regular bra size?
The measurements are the same, so your band and cup are a good starting point. The difference is in labeling: many sports bras use S, M and L, each covering a range of cups. Always translate your size through the specific brand’s chart, and do not size down hoping for more support.
How tight should a sports bra band be?
Snug enough that it stays level and does not ride up, with room for no more than two fingers between the band and your body. If it rises in the back or tissue shows under the cups when you raise your arms, try a smaller band. Do not rely on tight straps to make up for a loose band.
How often should I measure for a sports bra?
Every time you buy a new one. Weight changes, pregnancy, hormones and aging can all shift your size, and brands cut differently, so a quick re-measure prevents a bad purchase.