How to Measure for a Workout Bra | The 2-Tape Trick

Getting the right size for a workout bra comes down to two numbers and one simple subtraction. Measure your underbust for the band, measure your bust at its fullest point, then subtract. It takes about two minutes with a flexible tape measure, and it spares you the shoulder aches and chafing that come with a bra that’s off by even one size.

The catch is that sizing is rarely perfect on the first try. Different brands round differently, and a bra that fits at the store can shift after a few washes. Here’s the method that works across every major athletic brand, plus what to do when you land between sizes.

The Two Measurements You Actually Need

Grab a flexible tape measure and wear the least padded bra you own — or none at all. Padded or push-up bras distort the numbers, and adidas recommends measuring as close to your skin as possible.

1. Measure your band. Wrap the tape around your rib cage, just under your bust. Keep it level across your back and snug — firm enough to stay put, but never tight enough to leave a mark.
2. Measure your bust. Move the tape up to the fullest part of your chest, keeping it parallel to the floor across your back and breast apex. Again, snug but not squeezing.
3. Subtract. Take your bust measurement minus your band measurement.

That’s the core math. The rounding rules, however, vary by brand — and that’s where most people end up in the wrong size.

How Different Brands Handle Rounding

Each athletic brand has its own convention for rounding your measurements, so the same two numbers can point to different sizes on different charts. The safest move is to check the specific brand’s chart before you order, but these are the general rules:

• Round the band down:
• Round the bust up:
• Between sizes, go bigger: A slightly roomy band is easier to fix than one that digs in.

New Balance’s approach is simpler: wear your best-fitting unpadded bra, measure both points, and subtract — no rounding guidance mentioned. Title Nine takes yet another path, measuring your chest just under your arms and rounding an odd number up to the next even inch for the band. The takeaway is that brand charts aren’t interchangeable, and whichever label you’re buying from, its own chart is the one that counts.

Common Measuring Mistakes That Wreck the Number

Most sizing errors trace back to one of four consistent mistakes, all of which are documented in the official brand guides themselves:

• Measuring over a padded bra. The padding adds inches that aren’t you. adidas specifies no bra or a non-padded one that doesn’t change your breast shape.
• Letting the tape tilt. A tape that sags in back or rides up adds or subtracts real inches. Keep it level and parallel to the floor — that phrase appears in nearly every official guide for a reason.
• Pulling too tight. Nike, adidas, and Under Armour all explicitly warn against over-tightening. The tape should sit snug, never compress.
• Mixing rounding rules. Rounding your band up for one brand and down for another gives you a different letter. Pick one brand’s chart and follow its rounding instructions end to end.

Fit Checks That Confirm You Got It Right

Numbers get you close; a two-minute fit test confirms it. When you try the bra on, use the loosest hook setting first — you want room to tighten the band as the elastic wears over time. The cup should fully encase the breast tissue with no overflow at the top or sides. The center of the bra should sit flat against your sternum, and the band should stay level around your torso without riding up.

If the band is too tight or straps dig in, size up; if the band shifts or rides up, size down. And once you’ve found your size in one brand, don’t assume it transfers — Nike’s charts and adidas’s charts simply don’t match perfectly, so confirm with every new label you try.

For a closer look at the models that fit true to size and hold up wash after wash, check our roundup of the best women’s workout bras on the market before you order.