Fabric weight (GSM)
Also searched as: GSM, g/m2, gsm, grams per square meter, grams per square metre, mass per unit area, areal density, oz/yd2, ounces per square yard, ounces per linear yard, fabric mass
Fabric weight is mass per unit area, usually stated in grams per square meter (GSM, g/m2) or ounces per square yard, and sometimes misleadingly as ounces per linear yard.
In detail
Mass per unit area summarizes how much material a fabric contains, which correlates with properties such as opacity, warmth and durability but does not determine them. Standard methods cut specimens of known area from conditioned fabric and weigh them, or weigh full pieces of measured length and width. The figure depends on everything upstream: fiber density, yarn count, thread density, knit loop length and finishing shrinkage. Some sectors, notably denim, historically quote ounces per linear yard at the fabric's own width, which is not comparable across different widths.
The science and numbers
Mass per unit area equals specimen mass divided by specimen area after conditioning in a standard atmosphere, since fibers such as cotton and wool absorb moisture and gain mass. The unit conversion follows from 1 ounce being 28.35 grams and 1 square yard being 0.8361 square meters: 1 oz/yd2 is about 33.906 g/m2, the factor used in ASTM D3776/D3776M. Converting ounces per linear yard requires the width: oz/yd2 equals oz per linear yard divided by width in inches, multiplied by 36. ISO 3801 treats woven fabrics and distinguishes mass per unit length from mass per unit area, noting that for some structures these are not related simply by width. For a woven, areal mass can be estimated from ends and picks per centimeter, yarn tex values and crimp allowances.
A practical example
A catalog lists one T-shirt jersey at 200 g/m2 and another at 5.9 oz/yd2. These are essentially the same weight, since 5.9 multiplied by 33.906 is about 200. A denim sold as 12 oz per linear yard at 58 inches wide is a different case: dividing by the width and multiplying by 36 gives about 7.4 oz/yd2, or roughly 253 g/m2.
What to distinguish
Weight is not quality, thickness or warmth by itself. A lofty knit and a dense woven can share a GSM yet feel and perform very differently. Finished weight also shifts with moisture, washing shrinkage and finishing, so compare conditioned values measured by the same method. Always ask whether an ounce figure is per square yard or per linear yard.
Origins and history
Weighing cloth by the piece or by the running yard is long-standing trade practice because fabric was sold off the roll. International and national standards later fixed how to condition, sample and calculate: ISO 3801 for woven fabrics dates from 1977, and ASTM D3776 covers mass per unit area of fabric in both inch-pound and SI units. The metric GSM figure has since become the common language of international sourcing.
Related terms
Sources & further reading
- ASTM (via iTeh Standards): D3776/D3776M-20 Standard Test Methods for Mass Per Unit Area (Weight) of Fabric
- ISO: ISO 3801:1977 Woven fabrics, determination of mass per unit length and mass per unit area
- Threads Magazine: A matter of fabric weights
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.