GSM (grams per square meter)

GSM measures the mass of one square meter of fabric: cut a swatch, weigh it, do the math, and you get a number that scales with actual thickness and density regardless of fiber blend. Tee-weight fabric generally runs from about 120 GSM on the sheerest lightweight tees up past 220 GSM on heavyweight streetwear cuts, with most standard cotton and cotton-blend shirts landing somewhere in the 150–200 GSM band.

A Bella+Canvas 3001, at 4.2 oz, comes out to roughly 142 GSM; a Gildan 5000 at 5.3 oz lands around 180 GSM. Once you know a fabric’s GSM you can predict a lot without touching it — a 220 GSM cotton tee holds a crease and resists see-through printing in a way a 130 GSM tee simply can’t, no matter how good the ink is.

Almost every supplier outside the US, and a growing number of American mills, lists GSM as the primary spec on a tech sheet, right alongside or in place of ounces per square yard. Compare GSM across two blanks before comparing price — a cheaper shirt at a lower GSM will need a heavier ink deposit or an underbase to match the opacity of a pricier, denser one.

Buyers often assume GSM and oz/yd² are two competing measurements rather than the same physical quantity in different units — they convert directly, at roughly 33.9 grams per ounce, so a spec sheet quoting 5.3 oz and another quoting 180 GSM can be describing nearly identical fabric.