GSM stands for grams per square metre. It tells you how heavy a fabric is for a standard area, and it is widely used when buying knits, wovens and denim.

How it is measured

A circular sample of known area is cut from the fabric and weighed. The result is converted into grams per square metre. Some denim and woven fabrics are also given in ounces per square yard.

What it suggests

• Lower GSM is usually lighter and more breathable.
• Higher GSM is usually heavier and warmer.
• Weight often affects drape and structure.

Where GSM falls short

Two fabrics with the same GSM can feel very different because of fibre, yarn, knit or weave structure, and finishing. GSM is one data point, not a quality grade.

Tolerance is normal

Small differences between batches are common. Ask for an agreed tolerance and test the bulk fabric against it.

Use it well

Combine GSM with fibre content, construction and hand feel when comparing fabrics. Always ask for a physical swatch before ordering large quantities.

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