Sports Bra Sizing Guide | Measure Once, Fit Right

Most women wear the wrong sports bra size, and the culprit is usually a measuring tape that isn’t level or a band that’s too loose. The right sports bra does most of its work through the band—it should feel firm on the loosest hook, with cups that fully enclose you.

How To Measure For A Sports Bra: The Two-Number Method

Sports bra sizing comes down to two measurements: your band (underbust) and your bust (fullest point). The difference between them determines your cup size.

Step 1: Measure your band. Wrap a soft tape measure around your rib cage, just under your breast. Keep it level across your back and snug—but not squeezing. Round up to the nearest whole number. This number is your band size.

Step 2: Measure your bust. Move the tape to the fullest part of your breast, keeping it parallel to the floor. Round up again. Don’t pull tight—the tape should rest on your skin without compressing anything.

Step 3: Calculate your cup. Subtract your band measurement from your bust measurement.

Band And Cup Size Charts

Here’s how US guides typically map your underbust measurement to a band size, plus how the difference translates to a cup. Remember: these are starting points, not laws—brands vary.

*Cup letters beyond D depend on the brand—some use DD, others E.

Brand-Specific Fitting Tips

Each major brand adds its own twist to the basic method, so check the product’s chart before you order. Nike points out that not all its sports bra styles size exactly the same. adidas recommends measuring close to the skin—ideally without a bra or in a non-padded one. New Balance suggests wearing your best-fitting unpadded bra while you measure.

For the check, adidas says the band should be snug enough for a comfortable deep breath, and it shouldn’t rest on breast tissue.

Common Sizing Mistakes And The Fit Test

The biggest errors happen before you even read a chart. Measuring over a padded bra distorts the numbers. Letting the tape slope up or down throws off both measurements. And pulling it too tight produces a band size that will feel brutal after ten minutes of movement.

Once you’ve got a bra on, do the fit test. The band should stay level and firm when you raise your arms. Cups should fully enclose you—no spillover at the top or underarms. If you’re between sizes, most guides recommend sizing up for comfort, especially for sports bras, and buying two sizes to compare at home is a common fitting trick. The band does most of the support; a wired or compression top can’t fix a loose band.

When you’re ready to buy, our tested roundup of top sports bras breaks down which styles hold up for high-impact training versus everyday wear. For more detail on measuring, Nike’s women’s bra size guide and adidas’s sports bra size chart both walk through the same method with their own product-specific notes.