Two t-shirts can be identical in every measurement — same chest, same length, same shoulder — and behave like completely different garments. The variable nobody checks is the one that decides almost everything.
GSM stands for grams per square metre, and it is the weight of the fabric. It determines whether a dropped shoulder holds its line, whether a printed graphic stays legible, how a garment ages, and how many washes it survives before it stops looking like the thing you bought.
This is what the number means, what each range actually feels like, why it matters more on some garments than others, and how to use it when a listing does not mention it.
What GSM Measures
Take a square metre of the fabric and weigh it. That number, in grams, is the GSM. A 240 gsm cotton jersey means one square metre of that cloth weighs 240 grams.
It is a measure of density rather than thickness. A tightly knitted fabric can be heavier and thinner than a loose one, which is why weight predicts behaviour better than feel does — and why judging a garment by how thick it seems in a photograph does not work.
American listings sometimes use ounces per square yard instead. The conversion is roughly one ounce to 34 gsm, so a 7 oz tee is about 240 gsm and a 4.5 oz tee is about 150.
The Ranges, and What Each One Is For
120–150 gsm — lightweight
Summer tees, promotional garments, most fast fashion. Semi-transparent when worn, follows the body, and generally soft on first wear. It also loses shape quickly, shows every crease and cannot support a large print.
150–180 gsm — standard
The default for most high-street t-shirts. Opaque, reasonably durable, unremarkable. This is the weight most people have in mind when they think of a normal t-shirt.
180–220 gsm — mid-heavy
Where a garment starts to hold a shape of its own rather than describing yours. The first weight at which a dropped shoulder stays where the pattern put it.
220–260 gsm — heavyweight
The range used for oversized cuts and large graphics. It has visible body, hangs away from the torso, and keeps a back panel flat. Considerably warmer, noticeably stiffer for the first few wears, and the fabric most likely to still look right after two years.
Why Weight Decides the Silhouette
This is the part almost no styling guide mentions, and it undermines a lot of otherwise good advice.
An oversized cut is a pattern instruction: place the shoulder seam two to four centimetres past the shoulder point, deepen the armhole, widen the body. That instruction only survives contact with a body if the fabric is heavy enough to hang.
On light jersey the seam creeps back toward its natural position as soon as the garment is worn, and the drop quietly disappears. What is left is a garment that measures oversized and looks merely large — which is the exact failure people describe when they say an oversized tee looks sloppy on them.
The practical threshold is around 200 gsm. Below it, no amount of pattern work produces a reliable drop. Above it, the fabric does half the styling work on its own. We cover the rest of the silhouette question in this article.
What It Does to a Printed Graphic
Fabric weight affects printed artwork in three separate ways, and each one kills a different kind of design.
Creasing. A large back panel on light cotton folds across the shoulder blades every time you move. The artwork breaks along those folds and stops reading. Heavier fabric keeps the panel flat.
Ink absorption. A less dense fabric absorbs more ink and spreads it further. On fine linework, closely spaced black lines merge into a flat grey mass. On halftone, the dots bleed into each other and the image becomes mud. Both effects are invisible in a product photograph and obvious in person.
Stretch distortion. Any straight line, hard edge or geometric grid shows fabric movement instantly. A pixel grid, a checkerboard, a wireframe — these are the artworks that punish light fabric hardest, because the eye detects an irregular grid faster than an irregular drawing.
The Dark-Garment Problem
A consequence of density that gets almost no attention: heavier fabric holds dark dye better.
More fibre per square metre means more material holding pigment, so there is more to lose before the colour visibly shifts. A light black tee turns grey noticeably faster than a heavy one under identical washing.
This matters disproportionately in gothic and streetwear wardrobes, where black is the default and a faded black reads as worn out rather than as vintage. It is one of the least discussed reasons to pay attention to the number.
Weight buys you margin, not immunity. Cold water, inside out, no dryer, and no softener on printed areas — softener works by coating fibres, and a coated fibre holds less pigment. Heavy fabric washed carelessly still fades; it simply takes longer to get there.
Hoodies Work on a Different Scale
Fleece numbers are not comparable to jersey numbers, and treating them as one scale causes confusion.
A 300 gsm fleece is not "heavier than a heavyweight tee" in any meaningful sense — it is a different construction. Fleece is knitted and then brushed on the inner face to raise the fibres, creating air pockets that provide the warmth. The weight includes that lofted structure.
The useful range for a hoodie is 300 to 400 gsm. Below 300, the shoulder seam creeps back exactly as it does on a light tee and the oversized cut disappears. Above 450 you are into heavyweight loopback territory, which is excellent and considerably less comfortable indoors.
Everything in our hoodie collection sits in the 300 to 380 range, and the tees at around 240 — for the reasons above rather than as a specification exercise.
When a Listing Does Not Say
Most brands do not publish GSM, which is itself informative.
Absence usually means light. Nobody selling a 250 gsm garment hides the number, because it is a selling point. A listing that describes fabric only as "premium cotton" is describing marketing rather than material.
Look for substitutes. Some brands give ounces, some describe fabric as heavyweight or midweight, some publish the yarn count. Any number is better than an adjective.
Judge from photographs carefully. Look at how the garment hangs on a hanger and whether the hem falls straight or curls. Curling hems and clinging shoulders indicate light fabric regardless of what the description claims.
And treat the number as necessary rather than sufficient. A heavy fabric badly knitted from short-staple cotton will pill and go rough. GSM tells you how the garment will behave; it does not tell you how good the cotton is.
Questions People Actually Ask
What does GSM mean on a t-shirt?
Grams per square metre — the weight of one square metre of the fabric. It measures density rather than thickness, and it predicts how a garment hangs, how a print holds up and how the colour ages.
What is a good GSM for a t-shirt?
Around 180 to 220 for a standard fit with some substance, and 220 to 260 for an oversized cut or a large graphic. Below 200 an oversized pattern loses its dropped shoulder within a few wears.
Is higher GSM always better?
No. Heavier fabric is warmer, stiffer initially and less suited to hot weather. It is better for oversized cuts, large prints and longevity; it is worse for a summer tee you want to feel light in.
What GSM should a hoodie be?
Between 300 and 400 gsm for brushed fleece. Below 300 the shoulder seam migrates and an oversized cut stops reading. Fleece weights are not directly comparable to jersey weights because the construction is different.
How do I convert oz to GSM?
Roughly one ounce per square yard equals 34 gsm. A 7 oz tee is about 240 gsm; a 4.5 oz tee is about 150.
Why does my black t-shirt fade so fast?
Usually a combination of light fabric and hot washing. Denser fabric holds more pigment so takes longer to shift visibly. Cold water, inside out, no dryer and no softener extend it considerably.
