Your medium tights from one brand fit. The medium from another brand doesn’t. Neither company got it wrong.
The letter on the label is a market segment, not a measurement. Two garments can both say M and both fit, because they were cut for different amounts of stretch once they’re on you. Compare labels and you learn nothing. Compare measurements and you learn most of what you need.
Size charts hide the ease#
Most people read a size chart as a body measurement. Usually it’s a body measurement plus an intended ease.
A compression garment has negative ease: it’s cut smaller than the body it fits. A relaxed training top has positive ease: cut bigger. Both can carry the same letter. A chart that gives a chest range without saying which fit it means is half the information.
Compression changes the cut#
The fit is decided before the chart exists. A compression piece is cut small so the fabric stretches when worn, and the elastane and knit structure apply the pressure. A relaxed piece is cut big and the fabric does none of that work. Lululemon’s Align High-Rise Pant 25” is a useful reference: its Nulu fabric is 81% nylon and 19% Lycra elastane, and it usually runs $69–$98 depending on sales, per lululemon.com and Fleet Feet, Oct 2026.
That gap can be worth more than one size. A compression tight and a relaxed tight with the same stated waist can differ by several centimetres of flat fabric. So the compression pair feels too small out of the bag while fitting exactly as designed. The relaxed pair feels right out of the bag and hangs loose once it’s on.
Graded compression adds another twist: usually lower at the ankle or wrist, higher at the calf or thigh, and that change along the length is deliberate. If you’re used to relaxed sizing and order the same letter, you may find the ankle and thigh can’t both be comfortable. That means wrong letter, not a manufacturing fault.
Measure you, then measure it#
Two sets of numbers settle most cross-brand questions.
Body first. Stand relaxed, don’t hold your breath. Chest or bust at the fullest point. Natural waist at the narrowest point above the navel. Hips at the widest point. Then thigh at its widest, because in fitted bottoms the thigh often decides the size.
Then the garment. Lay it flat. Measure across the chest from armhole seam to armhole seam, and across the waistband edge to edge. Double those to get circumference. The difference between garment and body is the ease, and on compression it’s negative.
Run the math once and it clicks. A top with a 44 cm flat chest is 88 cm around. On a 92 cm bust that’s 4 cm of negative ease: a close fit, right for a knit with elastane. On an 84 cm bust the same top has 4 cm of positive ease: relaxed. Same number, two different garments. Only your body measurement tells you which one you bought.
Bottoms: inseam, rise, and the trap#
Bottoms go wrong across brands more often than tops, because length lives in two dimensions that charts describe loosely.
Inseam runs from the crotch seam to the leg opening. Two tights with the same letter and waist can differ by several centimetres here, which moves the hem on your calf or ankle. A hem landing on the widest part of the calf will ride up on a run.
Rise runs from the crotch seam to the top of the waistband, front and back measured separately. High rise sits at or above the natural waist and stays put when you move. Low rise sits below the hip crease and slides in a squat. Brands measure rise differently and some don’t publish it, so measure it on a pair you already own and like.
The drill: take your favorite pair, lay it flat, write down four numbers. Waistband width, front rise, back rise, inseam. Those four transfer between brands better than any letter.
Men’s and women’s charts#
Same bodies, different labels, and the cut differs beyond the letter. Men’s charts usually run on chest, waist and sometimes neck, with a straighter torso. Women’s run on bust, waist and hips, with shaping through waist and hip. Wear one chart’s garment on a body closer to the other and it often fits in one zone and not the next. Even the same jacket is cut and weighed differently by gender: Patagonia lists the men’s Houdini at 105 g and the women’s at 96 g, both about $119 at patagonia.com as of Oct 2026.
So ignore the category. Read the garment’s own measurements and its stated or photographed fit. If a piece comes in both and the body ranges overlap, pick the pattern with the shaping you need.
A repeatable routine#
- Write down your body measurements, thigh included, somewhere you’ll find them.
- Measure a garment that already fits well, flat, using the numbers for its category. Note fiber content too; elastane explains why it feels the way it does.
- Find the same flat measurements for the garment you’re eyeing, not just the size chart. Many listings show flat measurements beside body ranges. If only one is given, it’s usually the body range.
- Compare ease, not circumference. A few centimetres of difference between two garments with the same letter is normal. The question is which ease suits the session you’re buying for.
No measurements listed and a brand you don’t know? Honestly, the letter can’t predict the size. Waiting for a chart costs less than a return.
Keep a fit log#
Keep flat measurements for each category you buy: a training top, fitted bottoms, a compression piece, shorts. Fiber content goes in the same note, since it explains why two garments with identical numbers feel different.
Then read fit problems as data. A rolling waistband, a riding hem, a pulling shoulder: each points at one specific measurement. Sizing up rarely fixes a rise problem. Sizing down rarely fixes a loose armhole.