Quick Answer: Activewear sizes vary because brands use different base body measurements and different amounts of negative ease (how much smaller the garment is than your body) — always check the brand’s actual size chart in inches, not the letter size, before buying.

You wear a medium everywhere — except at 3 specific brands where you’re suddenly a small, and 2 others where you need a large. That’s not your body changing. That’s the industry having no shared standard for what ‘medium’ means.

Why don’t activewear sizes match across brands?

Because there’s no universal sizing standard for activewear, unlike some regulated industries. Each brand builds its size chart around a different fit model — a real person whose measurements become the baseline for ‘medium.’

On top of that, brands vary how much negative ease they build in (how much smaller the fabric is than your actual body, which is what creates compression). A brand with more negative ease will feel tighter at the same labeled size.

What should you actually check before buying?

Ignore the letter size completely on a new brand. Pull up their size chart and check 2 numbers: your waist or hip measurement in inches, and where you land on their chart, not the size you wear elsewhere.

If the brand lists both a ‘body measurement’ and a ‘garment measurement,’ the gap between them tells you the compression level — a bigger gap means tighter, more compressive fabric.

Myth vs Fact: Cross-Brand Sizing

Myth: Sizing is inconsistent because of poor quality control. Fact: It’s intentional design, not a mistake. Each brand’s fit model and ease amount are deliberate choices for their intended feel.

Myth: You should always size up when ordering a new brand online. Fact: Sizing up blind is just guessing in the other direction. Checking the actual chart takes 90 seconds and removes the guesswork entirely.

Myth: Reviews saying ‘runs small’ are reliable. Fact: ‘Runs small’ compares to the reviewer’s usual size at other brands, which varies person to person. Your own chart comparison is more reliable than any review.

How much should returns factor into your decision?

If a brand’s return window is under 14 days or charges a return fee, order 2 sizes on a first purchase from any new brand and return one — it’s often cheaper than 2 rounds of shipping guesses.

Once you know your number on that brand’s chart, every future order from them is a 30-second lookup, not a gamble.

FAQ: Activewear Sizing Questions, Answered

Should I trust a brand’s size chart over their size recommendation quiz?

The chart, generally — quizzes optimize for fewer returns, not perfect fit, and can nudge you toward whichever size is in stock.

Why do my measurements fall between two sizes on a chart?

Size up for compression leggings and structured pieces (which need room to stretch to fit), size down for relaxed, non-compression styles.

Does fabric content affect how true-to-chart a piece runs?

Yes — high-spandex blends (18%+) run closer to true-to-chart since they stretch to meet your body; low-spandex cotton blends run less forgiving, so size up if you’re between numbers.

TL;DR:

• Brands set their own fit models and ease amounts — there’s no shared activewear sizing standard
• Always check the brand’s own chart in inches, ignore the letter size from other brands
• A bigger gap between body and garment measurement means more compression, not a sizing error
• On a new brand’s first order, size 2 and return one if the return window is generous

The letter never tells the whole story — the chart does.

See It in Motion

Seen here: High Waist Yoga Leggings with Side Pockets — shop it on bubblelime.com