Fabric Weight: What GSM Tells You Before You Buy Online
The number is a weight, not a quality score
GSM stands for grams per square metre, and it is the weight of one square metre of the fabric. It is a physical measurement, not a judgment. A higher GSM means a heavier cloth. It does not mean a better cloth, a thicker cloth, or a warmer cloth, and the listings that treat it as a quality score are selling you a number, not a fabric. Two fabrics at the same GSM can feel entirely different, because the fiber, the weave, and the finish matter as much as the weight.
The ranges are the useful part. Light fabrics run 30 to 120 GSM: cotton voile at 40 to 100, a sheer summer blouse, a lining. Medium fabrics run 120 to 250 GSM: a cotton jersey tee at 120 to 220, a shirt, a dress. Heavy fabrics run 250 GSM and up: wool suiting at 250 to 350, a coat at 400 to 600. Read the range first, and the number second, because the range tells you what the fabric is for.
What to look for in the pieces you actually buy
A tee is the piece where GSM matters most, because a tee is the piece where the weight decides whether it drapes or clings, and whether it survives the wash. A cotton jersey at 120 to 150 GSM is a light summer tee, soft and breathable and prone to going sheer in white. A jersey at 180 to 220 GSM is a substantial tee, the one that holds its shape and does not go see-through. The listings that hide the GSM are usually hiding a light fabric at a heavy price, and the listings that print it are telling you what you are buying.
A shirt, a dress, and a coat follow the same logic. A shirt in a 120 to 150 GSM cotton is a summer shirt. A dress in a 200 to 250 GSM fabric is a dress with structure. A coat in a 400 to 600 GSM wool is a coat that keeps you warm, and a coat in a 250 GSM wool is a coat that looks like a coat and performs like a jacket. The number does not lie, which is why it is worth reading.
What GSM does not tell you
GSM does not tell you the thickness, because a loosely woven heavy fabric can be thicker than a tightly woven light one. It does not tell you the warmth, because a wool at 250 GSM is warmer than a cotton at 250 GSM, and a fabric with a brushed finish is warmer than the same fabric without one. It does not tell you the durability, because a tightly woven light fabric can outlast a loosely woven heavy one. And it does not tell you the hand, the way the fabric feels, which is the thing you actually care about when you wear it.
Use GSM as a filter, not as a verdict. Filter for the weight range that fits the piece and the season, then read the fiber content, the weave, and the reviews for the rest. A listing that prints the GSM, the fiber, and the weave is a listing from a seller who knows what they are selling, and that is worth more than any number on its own. For the fibers that fill most wardrobes, merino versus cashmere for winter covers the two that anchor a cold-weather capsule, and five outfits from one pair of dark jeans shows what a single heavy piece can do across a week.
Frequently asked questions
What does GSM mean in fabric?
Grams per square metre, the weight of one square metre of fabric. Light fabrics run 30 to 120 GSM, medium 120 to 250, and heavy 250 and up. It tells you how heavy the cloth is, not how thick or how good it is.
What GSM should a cotton tee be?
A cotton jersey tee sits around 120 to 220 GSM. At 120 to 150 it is a light summer tee, soft and breathable and prone to going sheer in white. At 180 to 220 it is a substantial tee that holds its shape.
Does a higher GSM mean better fabric?
No. A higher GSM means a heavier cloth, not a better one. Two fabrics at the same GSM can feel entirely different, because the fiber, the weave, and the finish matter as much as the weight.
What GSM is wool suiting?
Wool suiting runs 250 to 350 GSM, and wool coating runs 400 to 600 GSM. A coat in a 250 GSM wool looks like a coat and performs like a jacket, while a 400 to 600 GSM wool is a coat that keeps you warm.