Fabric GSM is the number most buyers quote when they argue about quality, and it is also the number most often quoted without context. GSM stands for grams per square metre: the weight of one square metre of fabric, measured on a conditioned sample with a calibrated scale. A 180 GSM t-shirt and a 240 GSM t-shirt can be knitted from the same yarn, on the same machines, in the same factory, and still feel like two different products in a customer's hand.
This guide covers what the number actually measures, how a mill tests it, where it drifts between the sample you approve and the bulk you receive, and how to write a GSM tolerance into a tech pack that a factory can be held to.
What GSM Actually Measures, and What It Does Not
GSM is mass per unit area. A specimen of known area is die-cut from the fabric, weighed to two decimal places, and scaled up to one square metre. That is the whole test. Everything else — yarn count, stitch density, fibre content, shrinkage, handle — is a separate specification that GSM does not capture.
Two fabrics can both read 200 GSM and behave nothing alike. A 200 GSM single jersey knitted from 30/1 combed cotton at a tight gauge has a dense, flat surface that holds a screen print crisply. A 200 GSM jersey from 20/1 carded yarn at a looser stitch length feels heavier in the hand, drapes more, and shows more surface texture after washing. The weight is identical; the fabric is not.
GSM also says nothing about the state the fabric was in when weighed. Greige fabric carries knitting oil and size; scouring and dyeing strip some of that mass, while compacting can add it back. A mill quoting greige GSM and delivering finished GSM can land 10 to 15 GSM away from what the buyer approved.
GSM to Oz/yd²: The Conversion Buyers Keep Getting Wrong
The conversion is simple: one ounce per square yard equals 33.906 GSM, so oz/yd² is roughly GSM divided by 33.9, or GSM multiplied by 0.0295.
| GSM | oz/yd² (approx) | Typical use |
|---|---|---|
| 120 | 3.5 | summer jersey, pocketing, linings |
| 150 | 4.4 | lightweight promotional t-shirt |
| 180 | 5.3 | standard retail t-shirt |
| 200 | 5.9 | heavier t-shirt, long-sleeve tee |
| 220 | 6.5 | mid-weight jersey, kids' sweat tops |
| 240 | 7.1 | heavy t-shirt, light sweatshirt, 2x1 rib |
| 280 | 8.3 | loopback sweatshirt |
| 320 | 9.4 | brushed fleece hoodie |
| 400 | 11.8 | heavy fleece, structured outerwear |
Two mistakes recur on purchase orders. The first is rounding: 180 GSM is 5.3 oz, not 5 oz and not 6 oz. Six weeks later, the gap between 5.3 oz and 6 oz is roughly 13 percent more yarn, and somebody has to absorb it.
The second is worse. Fleece is often sold in ounce language that describes the yarn fed into the machine, not the finished roll. A "10 oz fleece" and a 340 GSM fleece may be the same fabric, or 20 percent apart, depending on who is talking. Confirm that the number means finished weight, measured after relaxation, and get the test method in writing.
Why Knits and Wovens Report Weight Differently
Knitted fabric is elastic, so its weight depends on how relaxed it is when measured. A tubular single jersey pulled taut measures lighter per square metre than the same fabric lying flat and relaxed, because the loops are stretched out. This is why knit GSM should always be quoted in a defined state: greige, finished, or finished after a specified wash and tumble cycle.
Woven fabric is dimensionally stable enough that GSM is usually quoted alongside construction: yarn count, ends and picks per inch, and cuttable width. A 110 GSM poplin and a 240 GSM twill are both ordinary shirting weights, and both are specified with their construction because weight alone does not describe a woven fabric.
How a Mill Actually Tests GSM
The test takes minutes and is worth watching once, because it explains every weight dispute that follows.
If a mill cannot tell you the cutter area, the number of specimens, and whether the test was run before or after finishing, the quoted GSM is an opinion rather than a measurement.
Typical GSM Ranges by Product Category
| Product | Typical finished GSM | What drives the range |
|---|---|---|
| T-shirt, single jersey | 150–220 | print opacity, drape, summer wear |
| Polo, piqué | 180–240 | collar structure, wash durability |
| Sweatshirt, loopback | 280–340 | warmth without brushing |
| Hoodie, brushed fleece | 320–400 | loft, hand feel, cold-weather weight |
| Leggings, jersey with elastane | 220–280 | opacity under stretch, recovery |
| Kids' jersey | 140–180 | comfort, wash frequency, cost |
| Workwear twill (woven) | 200–260 | abrasion resistance, tear strength |
| Denim (woven) | 340–475 (10–14 oz) | structure, fade behaviour, season |
These are working ranges, not rules. A premium heavyweight tee at 260 GSM and a value retail tee at 160 GSM are both correct products; they are simply aimed at different shelves.
Sweaters are the exception that proves the point: they are specified by gauge and stitch rather than GSM, because a 12-gauge flat-knit jumper and a 7-gauge one differ in stitch size and yarn, and finished weight varies with panel shape as much as with fabric.
180 GSM vs 240 GSM: What the Difference Looks Like in the Hand
The step from 180 to 240 GSM is a 33 percent increase in yarn per square metre, and it changes more than weight.
At 180 GSM, a single jersey t-shirt is the standard export retail weight. It takes plastisol or water-based print well, holds a clean neckline if the rib is specified properly, and packs light. White at 180 GSM is usually opaque enough for retail; at 150–160 GSM, white starts to show through, and buyers either add a second layer or move up a weight.
At 240 GSM, the fabric has enough body to hold a boxy fit without clinging and reads as premium on a shelf. It also takes longer to knit, uses more yarn, adds freight weight, and needs a considered stitch length to avoid a stiff, boardy hand.
| Property | 160 GSM | 180 GSM | 220 GSM | 240 GSM |
|---|---|---|---|---|
| White opacity | marginal | acceptable | good | good |
| Drape and hand | light, clingy | balanced | substantial | heavy, structured |
| Print surface | tight mesh control needed | reliable | reliable | bold prints sit well |
| Yarn consumption | lowest | baseline | higher | highest of the four |
| Best fit for | summer basics, promotions | retail tees | premium tees, long sleeve | boxy heavy tees, sweatshirts |
Choosing between them is a product decision, not a quality decision. The quality failure is not "too light"; it is "lighter than the specification said, with the price unchanged".
Where GSM Moves Your Cost
Yarn is the largest single material input in a knitted garment, and yarn consumption scales roughly with GSM. Going from 180 to 240 GSM adds about a third more yarn per garment, before waste and before the extra knitting time on the machine. Dyeing a heavier load costs more per kilogram through the vessel. Freight is charged on weight, so a container of 240 GSM tees carries fewer pieces than the same container of 180 GSM tees.
That is why "reduce the GSM" is the most common cost-engineering move in the industry, and why it is worth resisting unless the product can carry it. A t-shirt dropped from 180 to 150 GSM to hit a landed cost target will photograph the same and disappoint in the hand: white that shows through, a neckline that softens after three washes, and a print that reveals every irregularity in the surface.
The honest version of that conversation is a trade-off, not a cut. If the target cost cannot support 180 GSM, the options are a denser knit, a shorter stitch length to protect opacity, a poly-cotton blend, or a cheaper yarn count — each with a hand-feel consequence that belongs on an approved swatch, not in a spreadsheet.
Where GSM Drifts Between Sample and Bulk
Weight problems almost never come from a mill lying about a test. They come from state changes nobody wrote down.
The defence is a written tolerance plus a cheap spot check: 180 GSM at plus or minus 5 percent finished, using a 100 cm² cutter on five specimens after the agreed wash cycle, then three specimens from three rolls weighed when bulk arrives. The test costs minutes; see-through white costs a season.
How to Specify GSM in a Tech Pack
Our guide to the tech pack for clothing covers the full document; the weight clause is one line of it, but it is the line that gets argued about most.
Getting Fabric Weight Right With Your Manufacturer
A factory that knits or directly sources its own fabric can usually hit a GSM target closely, because loop length can be adjusted before the roll is knitted. A factory that buys finished fabric from a mill has less room to move, and the honest answer to "can you do 240 GSM" is a mill confirmation, not a promise.
TEXVENTURE works as a Best Clothing Manufacturer in Bangladesh with more than 20 vetted partner factories, covering knitwear production, wovens, and sweaters. MOQ starts from 100 pieces per style, so a fabric weight trial is affordable at sampling stage rather than only at bulk. Partner factories hold garment factory certifications including ISO 9001, BSCI, OEKO-TEX, SGS, Sedex, and GOTS, which matters when a fabric claim has to be evidenced rather than asserted.
The workflow that avoids weight disputes is simple: approve the fabric on a measured swatch, confirm the specification through the garment sampling process before pre-production, and hold bulk to the written tolerance. Sourcing to shipping runs end to end, so the same specification travels from mill order to final inspection instead of being reinterpreted at each handover.
If you have a target weight and a target cost that need to reconcile before you commit, request a fabric weight and cost breakdown against your specification and we will price the realistic options rather than the convenient one.
Frequently Asked Questions
What GSM is good for a t-shirt?
For retail, 180 GSM single jersey is the working standard: opaque enough in white, holds a print, and survives washing without going limp. Premium and heavyweight tees sit at 220–240 GSM, while 150–160 GSM suits promotional and summer basics where light weight is the whole point.
Is higher GSM always better quality?
No. GSM measures weight, not quality. A 240 GSM fabric knitted from coarse, poorly spun yarn can pill and distort faster than a well-built 180 GSM jersey. Yarn quality, stitch density, dyeing, and finishing drive durability; GSM only says how much fibre sits in a square metre.
How do I convert GSM to oz fabric weight?
Divide GSM by 33.9, or multiply by 0.0295. So 180 GSM is about 5.3 oz/yd², 240 GSM is about 7.1 oz, and 320 GSM is about 9.4 oz. Confirm whether the ounce figure refers to finished fabric or to the yarn fed into a fleece machine, because the two are not the same measurement.
Why is my bulk fabric lighter than the sample?
Usually state differences rather than dishonesty: the sample was measured after compacting and the bulk before it, the specification quoted greige weight, or the bulk was weighed before a wash cycle the sample had already been through. A written tolerance with a defined test condition removes most of that ambiguity.
Can a factory adjust GSM without changing the design?
Yes, within limits. Loop length on the knitting machine can be adjusted to raise or lower weight by roughly 5–10 percent without touching the pattern, and yarn count can be changed for a larger shift. Beyond that the fabric construction changes, which needs a fresh swatch approval.