GSM stands for grams per square metre — it is the mass of one square metre of a fabric, and nothing more. It is a measure of weight, or density; it is not a measure of quality, and it is not a direct measure of thickness. A dense, fine-yarn knit and a loose, coarse-yarn knit can weigh exactly the same per square metre and still feel like different cloths in the hand.
What does GSM actually measure?
GSM records mass per unit of area. Take one square metre of a fabric, weigh it, and the figure in grams is its GSM. As a rule of thumb a heavier GSM means more yarn packed into the same area, which usually reads as warmer, more opaque and more durable, with a fuller, less fluid hand. It also tends to cost more and drape less freely.
What GSM is not is a grade of quality. A cheap knit spun from coarse, uneven yarn and a fine, tightly built knit can share an identical GSM and behave nothing alike — one may pill, twist and feel papery while the other holds its shape and handles well. Weight tells you how much fabric there is per square metre; it says nothing about how good that fabric is.
What controls a knit's GSM?
Several construction choices push GSM up or down, and they can offset one another:
- Yarn count — a finer yarn at the same settings lowers GSM; a coarser yarn raises it.
- Stitch or loop length — a tighter knit with a shorter loop packs more yarn into the area and weighs more; a slacker, more open knit weighs less.
- Machine gauge — the needle density of the knitting machine sets how fine the loop structure can be.
- Finishing — compacting, brushing and similar processes all change the final weight; a brushed or compacted fabric measures differently from its greige state.
The practical consequence is that two fabrics can arrive at the same GSM by entirely different routes — different yarn, different loop length, different finish — and differ in hand, drape and durability. GSM is an outcome of construction, not a substitute for describing it.
What are the typical GSM ranges?
The figures below are the ranges most often quoted for common knits. Treat them as typical rather than absolute; each can be pushed lighter or heavier for a particular end use.
| Fabric | Typical GSM | Common use |
|---|---|---|
| Single jersey | 110–180 | T-shirts, light tops |
| Pique / polo | 180–240 | Polo shirts |
| Interlock | 180–260 | Structured tops, kidswear |
| Rib | 200–320 | Cuffs, fitted styles — varies widely |
| French terry | 220–350 | Sweatshirts |
| Fleece | 250–350+ | Hoodies, joggers |
Rib is the widest-ranging of these, because it serves both as a light fashion fabric and as a heavy trim. Confirm the number rather than assuming it from the fabric name.
What about woven fabric and denim?
Weight for woven fabric, and denim in particular, is frequently quoted not in GSM but in ounces per square yard (oz/yd²). The two scales are directly convertible.
Converting oz/yd² to GSM
1 oz/yd² = 33.9 g/m². So a "12 oz" denim works out at roughly 12 × 33.9 ≈ 407 GSM. To go the other way, divide the GSM by 33.9.
At the light end, shirting weights sit around 90–130 GSM; bottomweights, twills and denims run considerably heavier. When a woven weight is quoted in ounces, convert it before you compare it with a knit specification, so you are reading one scale rather than two.
What are the common traps?
- Greige versus finished GSM differ. A fabric weighs one thing off the machine and another after finishing. Always state which figure you mean, and measure against the same state each time.
- GSM carries a tolerance. A commonly used band is ±5%. Agree the tolerance up front, in writing, rather than discovering it on the packing list.
- GSM alone does not fix performance. Shrinkage, spirality and hand are separate specification lines. A fabric can hit its GSM and still shrink or twist out of tolerance.
- Heavier is not automatically better. A higher GSM built from cheap, coarse yarn is not superior to a lighter, finer yarn knitted densely. Compare like with like before you read weight as value.
How do you choose a GSM?
Work backwards from the end use and the hand you want, not from a number in isolation. Decide what the garment has to do — a fluid summer tee, a structured polo, a substantial hoodie — and the weight band follows from that. Then let the knitter propose the construction, the yarn count and the loop length, that reaches it; they know their machines. Finally, approve the result against a physical swatch you have handled, not against the figure alone. A number on an enquiry and a fabric in the hand are not the same thing, and only the second one tells you whether the cloth is right.
GSM is where a fabric specification starts, not where it ends. It fixes the weight; the yarn, the construction and the finish decide whether the cloth actually does what you need — and none of those is captured by the number alone.
Because weight follows so directly from the yarn, GSM and yarn count are best specified together: the count you choose drives the GSM you can reach. On every fabric programme we pin the GSM, its tolerance and the finished state in writing before an order is confirmed, so the second roll is measured against the first rather than against a fresh conversation.
Tell us the weight and the hand.
Send the end use, the GSM band you have in mind and the finish you need. We will come back with the knitters genuinely able to hold it, and an honest view of price and lead time.