Sports Bras 101: How to Find Your Size at Home

Quick answer

Measure your underbust snugly and your full bust loosely with a soft tape, then subtract the underbust from the bust to estimate your cup. Round the underbust to the nearest even band size, and always check the bra's stated support level because a 34B in a light-support bralette will not fit like a 34B in a medium-support bra.

Most sports bra fit problems start before the bra ever arrives. If you guess your size from a everyday bra or order the same letter you wore years ago, you are working from stale numbers. A five-minute measuring session at home gives you a much better starting point.

This guide walks through the exact steps to measure sports bra size at home, then shows how to use those numbers when you shop. It also flags the sizing mistakes that send bras back, and points to real styles in our catalog so you can see how band, cup, and support level work together.

What you need before you start

You need a soft measuring tape, a mirror, and a non-padded bra or a fitted top. A soft tape follows the curve of your ribs and bust; a stiff builder's tape will give you a false reading. If you do not own a soft tape, use a piece of string or a phone charging cable, mark the length, then lay it against a ruler.

Wear the bra you would wear under activewear, not a push-up or heavily padded style. Padding adds volume that is not part of your measurement. If you are between sizes or your weight has changed recently, take fresh measurements rather than trusting a label from an old bra.

• Measure at the end of the day when your body is at its normal size, not first thing in the morning.
• Stand relaxed and breathe normally. Do not puff out your chest or suck in your ribs.

Step 1: Measure your underbust

Wrap the tape around your ribcage directly under your bust, keeping it level all the way around. The tape should sit snug against your skin without digging in. Breathe out normally and read the number where the tape meets. This is your underbust measurement.

If the number is odd, round to the nearest even number for your band size. For example, a 31-inch underbust usually points to a 32 band, while a 33-inch underbust points to a 34 band. The most common bra sizing mistake is pulling the tape too tight here, which makes the band feel smaller than it needs to be.

• Keep the tape parallel to the floor. A tape that dips at the back will read smaller than your true underbust.

Step 2: Measure your full bust

Wrap the tape around the fullest part of your bust, usually across the nipple line. Keep the tape loose enough that it does not compress breast tissue, but close enough that it stays in contact all the way around. Stand straight and look forward so your posture stays natural.

Read the number at the point where the tape meets. This is your full bust measurement. If you are measuring alone, do this in front of a mirror so you can check that the tape is level at the back. A bust measurement that is too loose or too tight will throw off your cup estimate.

• Do not measure over a padded bra. Padding adds inches that are not part of your body measurement.

Step 3: Calculate your cup estimate

Subtract your underbust measurement from your full bust measurement. Each inch of difference generally represents one cup size: about 1 inch for an A, 2 inches for a B, 3 inches for a C, and so on. For example, a 34-inch underbust and a 37-inch bust gives a 3-inch difference, which points to a 34C.

This is an estimate, not a guarantee. Cup fit also depends on breast shape, bra style, and how much compression the fabric provides. Use the number as a starting point, then adjust based on how the band and cups actually feel when you try the bra on.

• If your difference lands exactly between two cup sizes, order the larger cup for sports bras, since compression can make a too-small cup feel tighter.

Step 4: Match your size to the right support level

Band and cup are only half the story. Sports bras are built for different support levels, and the same size will feel different across styles. A light-support bralette is designed for low-impact movement and everyday wear, while a medium-support bra is built for training that includes jumping, running, or lifting.

Read the product description before you order. If a bra is described as everyday support or minimal support, size for comfort and coverage. If it is described as medium support, size for a secure fit that stays put through movement. This is where sports bra sizing at home pays off: you can compare your measurements against the stated support level instead of guessing.

• For high-impact workouts, look for compressive fabric and a band that stays level when you raise your arms.
• For yoga or walking, a softer band and removable padding are usually more comfortable.

Step 5: Check the fit before you commit

Once the bra arrives, do a five-point check. The band should sit level all the way around and stay in place when you lift your arms. The cups should lie flat against your chest without gaping or digging in. The straps should not slide off your shoulders or leave deep marks. The center front should sit against your sternum, not float away.

Move around in the bra before you decide. Jump, reach overhead, and bend forward. If the band rides up, the cups shift, or you feel pressure points, the size or the support level is wrong. A well-fitting sports bra should feel secure without restricting your breathing.

• If the band rides up at the back, go down a band size or choose a style with a firmer hem.
• If the cups gape, try a smaller cup or a style with removable padding you can adjust.

Your at-home sports bra sizing checklist

1. Measure underbust snug, not tight: Wrap a soft tape under your bust, keep it level, and breathe out before reading the number. Round odd numbers to the nearest even band size. If the tape leaves red marks, you pulled too tight.
2. Measure full bust without compressing: Wrap the tape around the fullest part of your bust, keeping it in contact but not pressing into tissue. Check in a mirror that the tape is level at the back before you read the number.
3. Subtract to estimate your cup: Full bust minus underbust gives roughly one cup size per inch of difference. Treat this as a starting point. Breast shape and bra style will shift the final fit.
4. Match size to stated support level: Read whether the bra is minimal, everyday, or medium support before choosing your size. A light-support bralette and a medium-support bra in the same size will not fit or feel the same.
5. Do the five-point fit check on arrival: Band level, cups flat, straps secure, center front against the sternum, and no pressure points. Jump and reach overhead. If the band rides up or the cups shift, exchange for a different size or support level.

How real styles map to your measurements

• Traction Bra - White: Medium support with a round scoop neckline, woven cross-over back straps, and a soft encased elastic hem. Available in sizes. A good reference point if your measurements point to a medium-support bra for strength training or higher-impact sessions. The encased elastic hem helps the band stay put, which is what you want when you are checking fit during movement.
• Dash Longline Bra - White: Extended length for added coverage, everyday support for light training or low-impact movement, strappy back design, compressive fabric, and seamless side panels to help reduce chafing. Available in sizes. Useful if your measurements suggest a light-support bra and you want more coverage through the torso. The longline shape sits lower on the ribs, so check that the band still lies level when you raise your arms.
• Honey Bralette - White: Made from sustainable recycled everyday fabric with a front scrunch detail, V-neckline, wide criss-cross back straps, and minimal support. Available in sizes. A realistic option if you want an everyday bralette rather than a training bra. Because support is minimal, size for comfort and coverage, not compression, and do not expect it to hold the same way as a medium-support style.

Measuring at home takes a few minutes and saves you from guessing. Start with your underbust and full bust, subtract to estimate your cup, then match that number to the support level the bra is actually built for. When in doubt, check the band first: it does most of the work in a sports bra.