GSM, Explained: The One T-Shirt Spec That Actually Matters

Pick up a product page for almost any t-shirt and count how many words are spent on feelings — "buttery," "elevated," "your new everyday." Now count how many give you a number. Usually one, if you're lucky. And it's almost never the one that matters.

The spec that actually predicts whether a tee survives two years of laundry is GSM — grams per square meter, the weight of the fabric. It's boring, it's measurable, and it's the single best honest signal you can read off a label. Which is exactly why so many brands don't print it. A missing weight is a tell.

What GSM is, and the three bands that matter

GSM is just how much a square meter of the fabric weighs. More grams means more cotton in the cloth, which generally means it drapes heavier, goes see-through less easily, and has more material to wear through before it thins out. Here's the whole map:

• —150–180 GSM — light. Thin, often slightly sheer, drapes close to the body. This is the standard budget-tee weight. Fine for layering or hot weather; the first to go translucent and lose its shape.
• —180–220 GSM — the sweet spot. Substantial enough to hold structure and survive the wash, light enough to wear year-round. If you only remember one range, remember this one.
• —220–260+ GSM — heavyweight. The thick, structured, "boxy premium tee" feel. Holds a crisp shape and stands up on its own. More fabric, more cost — and not automatically "better" for everyone (more on that below).

The useful part: when a brand *hides* the weight, they're almost always hiding a light one. A 230 GSM heavyweight is a selling point — they'll shout it. A 160 GSM tee priced like a premium one is something you quietly leave off the page. No number on the page is itself a data point.

The number they want you to look at instead

The headline spec brands love is the fiber — Supima, Pima, organic, "premium long-staple cotton." So here's the honest accounting: the raw cotton in any tee costs about $0.45 to $0.50. That's cotton at roughly 65¢ a pound and about two-thirds of a pound of fiber per shirt, counting the loss at ginning and spinning. The exact same ~$0.45 of cotton is sitting in a $6 tee and a $90 Supima tee.

Supima and Pima are real — US extra-long-staple cotton that pills less and feels smoother, a genuine fiber premium of roughly 15–50%. But 15–50% *on top of $0.45* is pennies. "You're paying for the cotton" is the most durable myth in apparel precisely because it's *almost* true. The cotton is better; it just isn't where the money goes. We did the same teardown for denim in "Premium Cotton," explained.

Where the cost actually shows up is the *fabric* — knitting and dyeing. A basic 160–180 GSM knit runs about $0.95–$1.10 in fabric; a premium 220–260 GSM combed ring-spun runs $2.50–$4. That swing — a couple of dollars — is most of the real material difference between a budget tee and a heavyweight one. Not the fiber name. The weight and the yarn.

Combed ring-spun vs. open-end: the second number to ask for

GSM tells you how much yarn is in the fabric. The *yarn type* tells you how good that yarn is, and it splits cleanly in two:

• —Open-end (carded) yarn is spun fast and cheap. Rougher, weaker, more prone to pilling. This is what's in most budget blanks — the Gildan 5000 (5.3 oz, carded, tubular) wholesales around $1.87–$2.78.
• —Combed ring-spun yarn is combed to remove short fibers, then twisted tighter. Smoother, stronger, softer, longer-lasting. The Bella+Canvas 3001 (4.2 oz Airlume combed ring-spun, side-seamed) runs higher — roughly $3–$10 depending on tier.

"Airlume," "combed ring-spun," "100s two-ply" — those are the words worth paying for. They describe construction you can't fake with a fiber name.

While you're reading the label, two more tells that cost the brand almost nothing to get right:

• —Side seams vs. tubular. A tubular tee (no side seams) is cheaper to cut and twists at the hem after a few washes. Side-seamed shirts hold their shape.
• —Banded ribbed collar + double-needle hems. A thin folded collar goes wavy; a ribbed, taped collar stays flat. Single-needle hems unravel where double-needle ones hold.

"Heavier is always better" is also a myth

Having just told you to read the weight, here's the catch: higher GSM is not a quality score. It costs more because it's literally more fabric, but a 250 GSM tee isn't "better" than a 200 GSM one — it's heavier. If you want a drapey summer tee, 240 GSM is the *wrong* choice, not the premium one. GSM predicts feel and structure. It predicts durability only alongside the yarn and construction — not on its own. Weight is a signal, not a trophy.

What the price tag does — and doesn't — tell you

Follow a tee from the factory floor. A basic cotton tee leaves the factory (FOB) at roughly $2.70–$3.96 — about $1 fabric, $0.80 labor, $0.60 overhead, $0.45 margin. Then keystone-plus markup takes over: COGS to wholesale (×2–2.5), wholesale to retail (×2–2.5), landing around 4–6× COGS. A ~$3 blank routinely retails $20–$30 printed. None of that markup is fabric. It's brand, channel, and margin.

Which is why price is a terrible quality proxy — and we don't have to take that on faith. The University of Leeds (LITAC), with WRAP, tested 47 t-shirts for durability and found no correlation between price and how long they lasted. Six of the top-ten performers cost under £15. The most durable tee retailed around £28. A £395 tee finished 28th out of 47. Weight and construction predicted durability; the price tag didn't. We unpack that study in do expensive t-shirts last longer.

This tracks with cost-per-wear, the only number that actually matters at the register. A $30 quality tee worn ~100 times runs about $0.30 a wear. A $6 fast-fashion tee that survives 10–15 washes runs $0.40–$0.60 a wear — *more*, despite the lower sticker, because it dies first. The cheap shirt isn't cheap; it's frequent.

How to read a tee in ten seconds

• —Find the GSM. 180–220 is the safe sweet spot. 150–180 is light; fine if you wanted light. 220+ is heavyweight; buy it on purpose, not by accident.
• —No GSM listed? Assume it's a light one and price it accordingly.
• —Look for combed ring-spun / Airlume, side seams, a ribbed banded collar, and double-needle hems. Those four cost the brand cents and tell you more than any adjective.
• —Ignore the fiber-name markup. Supima is real and nice; it's ~$0.45 of cotton plus pennies, not the reason for the price.

You can compare t-shirts by price tier on our side and see exactly where the weight and construction line up against the price — and the same logic runs one layer up in hoodies, where GSM matters even more.

The bottom line

GSM is the one t-shirt spec that survives contact with marketing. It's measurable, it maps to how the shirt actually wears, and when a brand omits it, that omission is information. Read the weight, then check the yarn and the seams — combed ring-spun, side seams, banded collar, double-needle hems. Those few facts cost the brand almost nothing and tell you nearly everything. The cotton is ~$0.45 either way, the price tag is mostly markup, and the Leeds data is blunt about it: what lasts is weight and construction, not the number on the tag. We explain how we pressure-test claims like these in how we review.