Guide
Fabric Weight and GSM, Explained
GSM is the fastest single number for understanding a fabric — and the one most often quoted wrongly, compared across incompatible units, or treated as a quality score.
What GSM measures
Grams per square metre: the mass of one square metre of the fabric. It is a density measure, independent of width, which is why it travels well between mills and countries.
The US alternative is ounces per square yard (oz/yd²). Roughly, 1 oz/yd² is about 34 GSM — so a 7 oz/yd² fleece is around 240 GSM. Keep one unit across a whole tech pack; mixing them is a reliable source of error.
Rough reference points for knits
- 110-140 GSM — lightweight jersey, drapey tees, layering pieces
- 140-180 GSM — standard t-shirt jersey; the bulk of the market
- 180-220 GSM — heavyweight tee, boxy structured fits
- 240-300 GSM — French terry, lighter sweatshirts
- 300-400 GSM — fleece and heavyweight hoodies
- 400+ GSM — very heavy fleece, outerwear-adjacent sweats
Treat these as orientation, not rules. Fibre, yarn and knit structure change how a given weight behaves — a 180 GSM combed ring-spun cotton and a 180 GSM carded open-end cotton are not the same cloth.
Ounces per linear yard: the one that misleads
Some suppliers quote weight per linear yard rather than per square yard. That number depends on the fabric’s width, so it is not comparable between fabrics of different widths. If a quote says “oz/yd”, ask whether it is square or linear before comparing anything.
Heavier is not better
Weight is a design choice, not a quality grade. A heavy tee feels substantial and sells well in some markets; it also costs more in fabric, takes longer to dry, and is wrong for a drapey silhouette. Plenty of expensive garments are light.
What does signal quality: yarn type and staple length, knit consistency, finishing, and shrinkage control. Those do not show up in GSM at all.
What weight does to your cost
Fabric is usually priced by weight, and it is usually the largest single line on a cost sheet. Moving from 180 to 220 GSM is roughly a 20% increase in fabric mass per garment, and it flows straight through to landed cost. It also increases freight weight on imported goods.
Specifying it properly
- State GSM with a tolerance — commonly around ±5%
- State whether it is finished weight or greige weight; they differ
- Record it in the BOM against the fabric line
- Verify the bulk against the approved sample, not just the swatch card
- Keep the unit consistent across the whole tech pack
Book a free discovery call and get a straight answer on your specific product.