Cotton Fabric GSM Guide: Choosing the Right Weight for Every Product

GSM — grams per square metre — is the fastest shorthand for how a cotton garment will feel and behave. It is also the most frequently mis-specified number in a tech pack, usually because it is quoted without a tolerance, without a finishing state, and without a yarn count.

Weight bands and what they are for

• 120–150 gsm: lightweight jersey. Summer tees, layering vests, muslin and babywear. Drapes softly, shows body shape, wears out fastest.
• 160–190 gsm: the global standard for a retail t-shirt. Opaque enough in most colours, stable through washing, works in both regular and oversized blocks.
• 200–230 gsm: premium tee territory. Holds structure, resists twisting, prints well with water-based inks.
• 240–280 gsm: heavyweight tee and lightweight sweatshirt crossover. Popular with streetwear brands for boxy blanks.
• 280–340 gsm: French terry and mid-weight fleece. Year-round sweatshirts and joggers.
• 360–420 gsm: heavyweight fleece. Winter hoodies. Requires dedicated heavyweight knitting machines and slower sewing to avoid needle damage.

Three specification traps

1. Finish state is not stated

Fabric is weighed greige, after dyeing, and again after compaction and brushing. A 300 gsm greige fleece can finish at 320 gsm after brushing brings the pile up, or drop below 290 after heavy enzyme washing. Always state whether the GSM target is finished or greige, and at what stage it is measured.

2. No tolerance is agreed

The commercially realistic tolerance for knitted cotton is ±5%. Tighter than that pushes fabric cost up sharply because the mill has to slow down and sort. Looser than ±7% and your garments will visibly vary between colourways and reorders. Write "180 gsm ±5%, measured on finished compacted fabric".

3. GSM is quoted without yarn count

A 200 gsm jersey in Ne 20 and a 200 gsm jersey in Ne 40 are different fabrics. The coarser yarn gives a more open, spongier hand; the finer yarn gives a denser, smoother surface. If you only specify gsm, mills will default to the cheapest yarn that reaches the weight — usually the coarser one.

How weight drives cost

Fabric is the largest single cost in a cotton garment, typically 45 to 60 percent of FOB. Weight scales almost linearly with fabric cost: moving a t-shirt from 180 to 220 gsm adds roughly 20 percent to the fabric bill and about 10 to 12 percent to FOB, before you account for slower sewing and higher freight weight. A 400 gsm hoodie uses more than twice the cotton of a 180 gsm tee, which is why heavyweight programmes are far more exposed to cotton price moves.

Weight and shrinkage behaviour

Heavier knits generally shrink less in percentage terms because the loop structure is tighter, but they take longer to dry and are more prone to seam puckering if the thread and needle are not matched to the weight. Lightweight jersey below 150 gsm is the most prone to spirality — the diagonal twist you see after washing — which is controlled by using compact yarn and setting the correct loop length rather than by increasing weight.

A practical specification line

"100% combed cotton, Ne 30/1 ring-spun single jersey, 180 gsm ±5% on compacted finished fabric, shrinkage ≤5% warp and weft after five home launderings to AATCC 135, pilling grade 4 to ISO 12945-2, OEKO-TEX STANDARD 100 class II." That one line removes most of the ambiguity that causes sample rejections.