GSM (Grams per Square Metre)

GSM, grams per square metre, is the mass per unit area of a fabric. It is a basic specification for woven, knitted and nonwoven fabrics and indicates how light or heavy a fabric is.

GSM is measured by cutting specimens of known area, often with a circular sample cutter, conditioning them in the standard atmosphere for textile testing and weighing them on a precision balance, then scaling the result to one square metre. Methods are described in standards such as ISO 3801 for woven fabrics and ASTM D3776. One ounce per square yard is approximately 33.9 grams per square metre.

Buyers and mills use GSM to specify and price fabrics and to check that production matches the approved sample. It relates directly to yarn count and thread density in woven fabrics, and to yarn count and stitch length in knitted fabrics, so changes in GSM often signal process drift.

Moisture content affects mass, so specimens must be conditioned before weighing, and samples are taken across the width and away from selvedges to be representative. GSM changes through finishing processes such as compacting, heat setting and washing, so the fabric state, grey or finished, must be stated. Tolerances on GSM are agreed between buyer and supplier.

Key points

Mass per unit area in grams per square metre
Measured by weighing conditioned specimens of known area
ISO 3801 and ASTM D3776 describe measurement methods
Changes through finishing, so the fabric state must be stated

Where AiVibe comes in

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Related terms

Terms that refer to GSM (Grams per Square Metre)

Warp KnittingTextile & Automotive Manufacturing