What Is GSM in Fabric? Fabric Weight Explained

Two t-shirts can both be labelled "100% cotton" and still feel completely different in your hands — one substantial and structured, the other thin enough to see through in bright light. That difference has a name: GSM, or grams per square metre, and it's one of the most useful, least-discussed numbers in clothing.

What GSM Actually Measures

GSM stands for Grams per Square Metre — a direct measurement of how much a single square metre of a given fabric weighs. It's a density measurement, not a size or thickness measurement on its own, though the two are closely related in practice: a higher GSM fabric is generally thicker, heavier, and more structured than a lower GSM fabric of the same material.

Why It's a Better Signal Than Price Alone

Fibre content on a label ("100% cotton") tells you what a fabric is made from, but not how much of it there is per square metre — which is exactly the gap GSM fills. A budget t-shirt and a premium one can share identical fibre content while differing significantly in GSM, which is often the real driver of how each one wears, drapes, and holds up over time.

Typical GSM Ranges by Garment Type

• Lightweight (under 150 GSM): Summer shirts, drapey blouses — breathable but generally less durable.
• Mid-weight (150–220 GSM): The sweet spot for most everyday t-shirts and shirts — a balance of comfort, structure, and durability.
• Heavyweight (220 GSM+): Sweatshirts, structured trousers, outerwear — built for durability and shape retention over breathability.

Higher GSM Doesn't Automatically Mean Better

It's a common misconception that higher GSM always equals higher quality. In reality, the right GSM depends entirely on the garment's purpose — a heavyweight summer t-shirt would be uncomfortably hot, just as an ultra-lightweight winter coat wouldn't perform its job. Fibre quality, weave construction, and finishing all matter alongside GSM, not instead of it.

Why GSM Matters More for Sustainable Fashion Specifically

Heavier, higher-GSM fabrics generally hold their shape and resist pilling far longer than lightweight equivalents — meaning a garment is more likely to be worn for years rather than a single season. This directly connects to our cost per wear guide: a higher GSM piece bought once often outperforms several lower-GSM replacements bought over time, both financially and environmentally.

How We Apply This

We choose fabric weights deliberately for each product category — substantial enough for durability in our trousers and outerwear, breathable enough for comfort in our tees and shirts. More on the full reasoning behind our fabric choices in Our Choice of Fabrics.

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