GSM, Explained Without the Marketing

GSM stands for grams per square metre. It's a measure of how much a fabric weighs per unit of area, and it's the single most useful number a brand can print about a garment. It's also the one most often left off.

What it measures

Take one square metre of the cloth. Weigh it. That's the gsm. A 200gsm cotton means a square metre of it weighs 200 grams.

Because area is held constant, gsm lets you compare two fabrics honestly. A 480gsm loopback has more than twice the material of a 220gsm jersey, whatever either label claims about being substantial or premium.

What it does not measure

This is where people get burned. GSM tells you mass per area. It says nothing about:

• Fibre quality. Short staple cotton and long staple cotton can weigh exactly the same and wear completely differently. Short fibres work loose and pill.
• Construction. A knit and a woven at the same weight behave nothing alike.
• Finish. Some mills add weight with sizing or coating that washes straight out. The garment gets lighter after the first wash and thinner every wash after.
• How it was cut and sewn. Heavy cloth in a badly built garment still fails at the seams.

So gsm is necessary and not sufficient. Use it to rule things out, not to declare a winner.

Useful ranges, by garment

Numbers worth carrying around:

• T shirts. 140gsm is a summer tee you can see through. 180 to 200gsm is a good everyday weight. 220gsm and up is a boxy, structured tee that holds its shape.
• Hoodies and sweats. 280gsm is light, 350gsm is standard, 420gsm and up is genuinely heavy.
• Denim. Measured in ounces per square yard instead, out of habit. 12oz is light, 14oz is standard, 16oz and above is heavy and takes months to break in.
• Knitwear. Usually sold by gauge rather than gsm, but a lambswool crew around 400 to 500gsm is a real winter garment.

Why brands hide it

Because it's checkable. A page that says premium heavyweight cotton is making a claim nobody can test. A page that says 480gsm is making one that a customer with a kitchen scale and a ruler can verify. The second kind of claim is harder to make and worth more.

When a spec sheet lists gsm, thread count, and the mill, you're usually dealing with someone who knows their supply chain. When it lists adjectives, you're dealing with marketing.

The short version

Ask for the number. Compare within a category, not across one. Treat gsm as a floor test rather than a quality score, and then look at the fibre and the seams.

Every product we list carries its weight in the spec line. If you want the longer argument about hoodies specifically, we wrote what actually counts as heavyweight. Otherwise the cloth is on the shop page.