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Fabric GSM

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Grams per Square Metre

A measure of fabric weight and density expressed in grams per square metre, used to judge how thick, warm, or durable a textile is.

Definition

Fabric GSM (grams per square metre) measures how much a given area of fabric weighs, which serves as a proxy for thickness, density, and durability. A lightweight summer shirting fabric and a heavy winter coat lining can look similar on a hanger, but their GSM numbers tell you immediately which is which.

It's one of the most commonly quoted specs in textile manufacturing and sourcing, letting buyers compare fabric weight consistently across suppliers regardless of the fabric's fibre content or weave pattern. Convert between GSM and other weight units with the Fabric GSM Converter.

Formula

GSM = Sample Weight (grams) ÷ Sample Area (square metres)

Worked Example

A 10 cm × 10 cm swatch (0.01 square metres) weighs 1.8 grams on a lab scale. Scaling that up: 1.8 ÷ 0.01 = 180 GSM, a weight typical of a mid-weight cotton t-shirt fabric.

Key Things to Know

  • Rough GSM bands by use case: shirting fabric often sits around 100-150 GSM, t-shirts around 150-200 GSM, hoodie fleece around 280-400 GSM, and heavy denim can exceed 500 GSM.
  • GSM affects drape and warmth as much as durability. Lightweight fabrics flow and breathe better; heavier fabrics hold structure and insulate more, which is why the "right" GSM depends entirely on the garment's purpose.
  • Knits and wovens with the same GSM can feel very different. Weave or knit structure changes how a fabric handles and stretches even at an identical weight, so GSM alone doesn't fully describe a fabric's hand-feel.
  • Suppliers sometimes quote GSM inconsistently across regions, occasionally mixing it up with ounces per square yard in export documentation, which is where a reliable conversion becomes genuinely useful rather than just a formality.

Frequently Asked Questions

Most cotton t-shirts fall between 150 and 200 GSM, with budget shirts often around 120-140 GSM and premium heavyweight tees closer to 220-240 GSM. Higher GSM generally means a thicker, more durable fabric that holds its shape better after repeated washing.
They cut a fixed-size circular or square swatch, usually 100 square centimetres, weigh it precisely on a lab scale, and scale the result up to a full square metre. This is more accurate than estimating from a full roll of fabric, since thickness can vary slightly across a large piece.
Not necessarily, GSM measures weight and density, not fibre quality, weave tightness, or how the fabric will feel against skin. A well-made 150 GSM fabric can outlast a poorly constructed 250 GSM one, so GSM is one input among several, not the sole quality signal.
Bedsheets are typically much lighter, in the 130-200 GSM range for good breathability, while towels run far heavier, often 400-900 GSM, since absorbency and plushness matter more than lightness there. The right GSM depends entirely on what the fabric needs to do.
Yes, this is common when comparing fabric specs between suppliers using metric versus imperial standards, particularly in denim and workwear. The [Fabric GSM Converter](/fabric-gsm-converter/) handles this conversion directly.