GSM appears on product pages constantly and most shoppers have no idea what number is good. GSM means grams per square metre — a measure of fabric weight and density that tells you how substantial a garment feels — but heavier isn't automatically better, just different.
What GSM actually measures
Straightforwardly: the weight in grams of one square metre of fabric. Higher means heavier, denser, usually thicker. It's the international metric; US brands sometimes quote ounces per square yard instead — the same property, different units, with 1 oz/yd² a little under 34 GSM. That's why a "3.8 oz" tee and a "130 GSM" tee describe similar territory. What GSM tells you is weight and substance — not fibre quality, softness, or durability.
Typical ranges
Rough guides for t-shirts. Under ~130 GSM — lightweight; thin, drapey, sometimes semi-sheer, common in fashion tees and triblends. ~140–180 GSM — midweight; the standard everyday t-shirt range. ~180–220 GSM — heavyweight; thick, opaque, structured, the "premium heavyweight tee" territory. Over ~220 GSM — very heavy and boxy, closer to a light sweatshirt. Hoodies typically run 250–450 GSM, with 300–350 a common midweight.
Heavier isn't automatically better
The point most GSM discussion misses. Heavyweight has become a marketing signal for quality, but weight and quality are different things — a poorly made 220 GSM tee is worse than a well-made 140. More usefully, each weight suits a different purpose: heavyweight is structured and boxy, good for an oversized silhouette but warm and less drapey; lightweight is cooler, drapes closer, and layers better, but shows more underneath. Choose for use and look, not on the assumption that bigger is better.
What GSM doesn't tell you
Fibre quality — nothing about whether the cotton is combed and ring-spun (smoother, stronger) or open-end (coarser, cheaper); two tees at identical GSM can feel entirely different. Construction — knit, stitching, and finishing affect durability and feel. Softness — a heavy fabric can be rough, a light one luxurious. Composition — a 150 GSM triblend and a 150 GSM cotton tee behave differently. GSM is one data point about substance, not a quality score.
Blends and performance fabric
Two contexts worth knowing. Blends like triblend sit at the lighter end — often 130–150 GSM — because rayon and fine yarns produce a light, drapey fabric by design; the softness comes partly from being lightweight. Performance fabrics are light too, since low weight supports quick drying and breathability. For both, lower GSM is the correct specification rather than a compromise — worth knowing before dismissing a shirt as "thin." See cotton vs polyester.
Quick answers
What does GSM mean?
Grams per square metre — the weight of one square metre of fabric.
Good GSM for a t-shirt?
140–180 for everyday; 180–220+ heavyweight; under 130 lightweight.
Is higher better?
Not automatically — heavier is structured and warm, lighter is cooler and drapier.
GSM to ounces?
Roughly 1 oz/yd² ≈ just under 34 GSM.
Hoodie GSM?
Typically 250–450.
Does GSM indicate quality?
No — it measures weight, not fibre or construction.
Why are triblends low GSM?
Their lightness is intentional and creates the drape.
GSM tells you how heavy a fabric is. It tells you nothing about whether it's good — which is why a great 140 beats a mediocre 220 every time.
GSM is grams per square metre, with everyday tees typically 140–180 and heavyweights 180–220+. Genuinely useful for knowing what you're buying, but it measures substance rather than quality — and lightweight fabrics like triblend and performance materials are light by design. Read it alongside fibre content and construction.