A sports bra that fits well disappears. You forget it's there until you're mid-set and it's still doing its job, no adjusting, no digging straps, no bounce you're managing instead of your workout. A sports bra that fits badly announces itself constantly, and most people wearing one have no idea it's the bra, not their body, causing the problem.
Check these four things.
The band: your main support, not your straps
The band, not the straps, should provide most of the support. If you're relying on tight straps to hold everything in place, the band is too loose, and no amount of strap tightening will fix that properly.
The test: the band should sit level, parallel to the floor, snug enough that you can only fit two fingers underneath it. If it rides up your back during movement, or you can pull it more than a couple of centimetres away from your ribcage, size down the band.
The straps: adjustable, not load-bearing
Straps should stay in place without digging into your shoulders or slipping down mid-set. You should be able to fit two fingers under each strap comfortably. If they're leaving deep red marks by the end of a session, they're taking on support the band should be providing, which usually means the band size is wrong, not the strap length.
The cups: full coverage, no spillage, no gaping
Whatever the style, breast tissue shouldn't spill over the top or sides of the cup, and there shouldn't be loose, gaping fabric either. Both signal the wrong cup size, and cup sizing varies more between sports bra brands and styles than it does in everyday bras, so don't assume your regular bra size translates directly.
How to measure yourself properly
Measure your band size first: wrap a tape measure snugly around your ribcage, directly under your bust, keeping it level and parallel to the floor. Then measure around the fullest part of your bust. The difference between the two numbers roughly indicates cup size, though this varies by brand, so treat it as a starting point rather than a final answer, and always check the specific size guide for the style you're buying.
Matching support level to your training
Not every session demands the same support, and over-supporting for low-impact training or under-supporting for high-impact work both create problems.
Low impact (yoga, walking, strength training): a compression-style or lighter bra usually gives enough support without unnecessary bulk. Our halterneck bras work well here, giving shape and light support for training that doesn't involve much vertical movement.
Medium impact (weight training, cycling, HIIT): a mid-support encapsulation or combination bra handles the movement without the bulk of a full high-impact style.
High impact (running, Hyrox, plyometrics, burpee broad jumps): this is where support matters most, and where the wrong bra becomes obvious fastest. If you're prepping for race day, this is the category worth getting right before you're mid-station finding out the hard way.
Fitting for a bigger bust
A bigger bust needs wider straps, a firmer band, and genuine encapsulation (individual cup structure, not just compression fabric squashing everything flat). Compression-only styles often aren't enough support on their own for a fuller bust during high-impact training, even if the sizing technically fits. Our sports bras for big bust are built with the structure that this demands, not just a bigger version of a compression style designed for a smaller frame.
Signs your current bra doesn't fit, even if it feels fine standing still
Fit problems usually only show up in motion. Check for: the band riding up during a run, straps sliding off during overhead movement, bounce you're consciously trying to control, or a band mark that's still visible an hour after you've taken it off. Any of these means it's worth reassessing size or style, even if the bra felt fine when you tried it on standing still in front of a mirror.
Different styles for different training
Our backless sports bras work well for lifting and lower-impact training where an open back doesn't compromise support. For high-impact work, prioritise structure and band security over style, and check the specific support rating rather than assuming all bras in a range perform the same under load.
Getting this right isn't vanity. A sports bra that fits changes how a session feels from the first rep, and most people who think they've "always been like this" during high-impact training are one correctly fitted bra away from finding out they hadn't.