GSM stands for grams per square meter, and it is the single most useful number on a clothing spec sheet. It tells you how heavy and how structured a fabric is before you touch it.
Lightweight knits at 140-180 GSM suit summer tees and linings. Mid-weight 200-260 GSM covers everyday basics and layering. Heavyweight 280-320 GSM tees and 380-450 GSM fleece give the structured drape streetwear brands build collections around.
T-shirts: 240-320 GSM for streetwear, 180-220 GSM for basics. Hoodies: 380-450 GSM brushed fleece for heavyweight programs. Shorts: 240-300 GSM jersey or fleece, mesh for performance. Jerseys: 120-150 GSM mesh for matches.
Heavier is not automatically better. What matters is the yarn quality, knit structure and finish. Two 280 GSM tees can feel completely different if one uses combed long-staple cotton and the other uses carded yarn with filler.
Write GSM into your tech pack alongside the fabric name, like "280 GSM combed cotton single jersey, pre-shrunk". Ask for a swatch card or reference sample, and confirm shrinkage after washing before approving bulk.