I misstated the definition a bit, although in real world terms a higher GSM does often manifest as a thicker cloth. GSM stands for grams per square meter. It measures how much fabric weighs in a given area. It is a weight rating, not a thickness rating.

Higher GSM means denser, heavier fabric. Lower GSM means lighter, more breathable fabric.

General guide:

120–140 GSM = lightweight (summer sheets, thin shirts)

150–170 GSM = medium weight (jersey sheets, linen duvet covers)

180–250 GSM = heavier weight (flannel, winter bedding)

GSM helps compare feel and durability across materials, but thickness will vary by fiber type.