GSM is grams per square metre: the weight of one square metre of the cloth. It is the fastest way to place a fabric — it tells you roughly what season it belongs to, what it will cost to ship, and what kind of garment it can carry. That is why it appears on every specification sheet, and why buyers reach for it first.
What GSM genuinely tells you
Weight correlates strongly with opacity, drape and durability within a single construction. A 120 GSM cotton poplin and a 180 GSM cotton poplin are recognisably the same kind of cloth at different weights, and the heavier one will be more opaque, more substantial in the hand and longer-wearing. Within a category, GSM is a reliable shorthand.
Where it misleads
Across constructions, GSM stops being comparable. A 180 GSM linen and a 180 GSM single jersey weigh the same and behave nothing alike: one is a woven shirting, the other a knitted T-shirt cloth with stretch in both directions. Comparing them by weight alone tells you nothing useful.
The more expensive mistake is treating GSM as a quality signal. Two cotton poplins at 120 GSM can differ by a factor of three in price, and the difference is yarn count. A fine two-fold yarn produces a smooth, lustrous, durable cloth; a coarse single yarn at the same weight produces something noticeably rougher. The scale cannot see the difference. Your customer will.
Width belongs in the same sentence
GSM prices a square metre, but production consumes linear metres. A cloth quoted at 150 cm width yields materially more usable fabric per metre than one at 140 cm, and on a marker with pattern pieces that do not nest neatly, that difference can exceed the price gap between the two cloths.
- GSM
- Weight per square metre — season, opacity, durability
- Yarn count
- Fineness of the yarn — hand, lustre, price tier
- Width
- Usable cloth per linear metre — real consumption
- Construction
- Woven or knitted, and in which structure
How to quote properly
Ask for all four together. "120 GSM cotton poplin" is an incomplete request; "120 GSM cotton poplin, 2/100s, 150 cm" is a specification a supplier can price and reproduce twelve months from now. The extra two figures cost nothing to state and remove most of the ambiguity that produces disputes later.
- Compare GSM only within the same construction.
- Ask for yarn count alongside weight in wovens.
- Calculate cost per garment, not cost per metre.
- For knits, remember weight is quoted relaxed — it moves.
A note on knits
Knitted fabrics complicate this further, because a knit is quoted at its relaxed weight and a knit does not stay relaxed. Tension on the roll, the finishing route and how long the cloth has rested all shift the measured figure, and a jersey quoted at 180 GSM can measure noticeably differently once it has been allowed to sit. This is why relaxation before cutting is standard practice rather than a precaution: cutting a knit straight off the roll produces twisted side seams and garments that shrink unevenly, and no GSM figure on a specification sheet warns you about it.