What GSM means
GSM is the mass of one square metre of fabric in grams. A 180 GSM jersey weighs 180 g per square metre. It is also written g/m², and test standards call it mass per unit area. It is the main fabric weight figure because it is quick to test and easy to compare, and because knitted fabric is usually bought by the kilogram.
GSM tells you weight, not quality. Two fabrics of the same GSM can differ in fibre, yarn, construction and finish, so always state GSM beside composition and construction.
How GSM is measured
The quick factory method uses a GSM cutter, a round cutter that takes a sample of exactly 100 cm². Weigh the sample on a balance reading to 0.01 g and multiply by 100: a sample of 1.80 g means a 180 GSM fabric.
- Condition the fabric first, because moisture adds weight. Laboratories use a standard atmosphere; ISO 139 sets 20 degrees C and 65 percent relative humidity.
- Lay the fabric flat without tension and cut several specimens across the width, away from the selvedge and folds.
- Report the average, with the highest and lowest result.
For contracts and disputes, name a laboratory method. ASTM D3776/D3776M covers mass per unit area of fabric, with options for full rolls, full-width samples and small swatches. ISO 3801 covers woven fabrics, and EN 12127 covers small specimens of woven and knitted fabrics. A small swatch result describes that swatch, not the whole lot.
GSM tolerance
Plus or minus 5 percent is a common commercial tolerance, which on a 180 GSM fabric allows 171 to 189 GSM. Some buyers set a tighter band where weight drives hand feel or price, or a one-sided limit such as no lower than the stated GSM. Agree it before fabric is bought.
Apply the tolerance to the average of several specimens and state the stage: finished fabric before cutting, or the garment after washing. Washing changes dimensions, so a fabric inside tolerance on the roll can fall outside it after an enzyme wash.
Typical GSM by garment
These are common industry ranges, not limits. The right GSM for your range is the one you specify, and we produce to it.
| Garment | Usual fabric | Typical GSM |
|---|---|---|
| T shirts | Cotton single jersey | 140 to 220 |
| Heavyweight T shirts | Cotton single jersey | 220 to 300 |
| Polo shirts | Cotton pique | 180 to 240 |
| Performance tees | Polyester jersey or mesh | 120 to 180 |
| Sweatshirts and hoodies | French terry or brushed fleece | 240 to 400 |
| Formal shirts | Cotton poplin, oxford, twill | 90 to 160 (cotton formal shirts typically 100 to 140) |
| Chinos and trousers | Cotton twill | 200 to 300 |
| Jeans | Denim | 10 to 14 oz (about 340 to 475) |
| Jackets | Cotton twill or canvas | 250 to 400 |
| Kids T shirts | Cotton single jersey | 140 to 180 |
| Babywear | Cotton poplin, muslin or jersey | 60 to 200 |
Ribs and collars are separate fabrics with their own weight, so list them separately. See our products for fabrics by style.
GSM and ounces
Denim, canvas and many US listings use ounces per square yard (oz/yd²). 1 oz/yd² is about 33.906 GSM, so multiply ounces by 33.906 to get GSM, or divide GSM by 33.906 to get ounces. A 12 oz denim is about 407 GSM.
| oz/yd² | GSM (approx.) | Where you see it |
|---|---|---|
| 3 | 102 | Lightweight shirting |
| 4 | 136 | Shirting and light jersey |
| 5 | 170 | Standard T shirt jersey |
| 6 | 203 | Heavier jersey and pique |
| 8 | 271 | Twill for chinos, fleece |
| 10 | 339 | Light denim, canvas |
| 12 | 407 | Mid-weight denim |
| 14 | 475 | Heavy denim |
Two cautions: denim weight is often quoted before washing, and some suppliers quote ounces per linear yard at a stated width, which is not the same as per square yard. Ask which one you are given.
Why the same GSM can feel different
GSM is the result of several choices. Change one and a fabric of the same weight can feel thicker, smoother, stiffer or more open.
- Yarn count. Cotton count (Ne) rises as yarn gets finer. A fine yarn used densely can match the GSM of a coarser yarn used openly, but feels smoother and prints more cleanly.
- Construction. In knits, the structure (single jersey, pique, interlock, rib) and loop length; in wovens, the weave (plain, oxford, twill) and the thread count, the ends and picks per inch.
- Yarn type. Combed and ring-spun yarns are smoother than carded or open-end yarns. Two-ply yarns, common in premium shirting, are more even and stronger.
- Fibre. Polyester is less dense than cotton, so it is slightly bulkier at the same GSM. Elastane adds weight and stretch recovery.
- Finishing. Brushing, peaching, mercerising and softeners change the hand feel and can move GSM.
So specify "100 percent combed cotton single jersey, 30s Ne, 150 GSM", not "150 GSM cotton".
How GSM drives garment cost
Knitted fabric is usually bought by the kilogram, so:
Fabric cost per garment = consumption in m² × GSM ÷ 1,000 × price per kg
Consumption is the fabric area per garment, including cutting waste. The example is illustrative: 1.0 m² per adult T shirt and 5.00 per kg in any currency. These are not GoodBiz prices or quotes.
| GSM | Fabric per garment | Fabric cost per garment | Fabric cost per 3,000 pieces |
|---|---|---|---|
| 160 | 0.160 kg | 0.80 | 2,400 |
| 180 | 0.180 kg | 0.90 | 2,700 |
| 220 | 0.220 kg | 1.10 | 3,300 |
Here 220 GSM uses 22 percent more fabric than 180 GSM. Real costs are rarely that linear: fine combed yarns cost more per kg than coarse ones, and special dyes or finishes add cost. Woven shirting is usually priced per metre at a stated width instead. Heavier garments also add carton weight, which matters for air freight.
Choosing GSM by climate and market
These are typical patterns, not rules.
- Hot, humid markets such as the Gulf, much of Africa and Australian summer ranges favour T shirts around 140 to 170 GSM and lighter shirting. See UAE and GCC, Africa and Australia.
- Temperate markets such as the UK, northern Europe and much of the USA use T shirts around 160 to 200 GSM most of the year, with heavier fleece and twill in winter. See UK, Europe and USA.
- Premium and streetwear ranges often use jersey of 220 GSM and above.
- Kidswear stays light and soft, commonly 140 to 180 GSM for T shirts, but must survive frequent washing.
The simplest benchmark is your own best seller: measure it and start there.
Shrinkage, finishing and GSM
GSM changes during processing, so greige fabric, finished fabric and the washed garment can all differ.
- Compacting knits and sanforising wovens pre-shrink fabric before cutting, which reduces later shrinkage and usually raises GSM slightly.
- Washing shrinks unstabilised fabric. The same mass then covers less area, so GSM rises; garment and enzyme washes do the same.
- Brushing and peaching can shift GSM by a few percent.
Specify shrinkage with GSM. It is commonly tested with ISO 5077 using an ISO 6330 wash cycle, or in the USA with AATCC TM135 for fabrics and AATCC TM150 for garments. Many buyers set limits of around 5 percent for knits and 3 percent for wovens, plus a twist (spirality) limit for single jersey.
How to write GSM into a purchase order
Put GSM in the tech pack, the purchase order and the approved sample record, so it can be checked at inspection. Give composition, construction and yarn, GSM with tolerance and stage, width for wovens, finish, shrinkage limit and colour standard. For example:
"Body fabric: 100 percent combed cotton single jersey, 24s Ne, 180 GSM plus or minus 5 percent after finishing, compacted, reactive dyed, dimensional change within 5 percent to ISO 6330 and ISO 5077."
Not sure? Send a garment you already sell. We measure its GSM and put it in a spec sheet for your written approval. See also how to send a tech pack.
Sources and official links
- ASTM D3776/D3776M: Standard Test Methods for Mass Per Unit Area (Weight) of Fabric
- ISO 3801: Woven fabrics, determination of mass per unit length and mass per unit area
- BS EN 12127: Fabrics, determination of mass per unit area using small samples
- NIST Guide to the SI, Appendix B.8: Conversion factors
- ISO 5077: Determination of dimensional change in washing and drying
- AATCC TM150: Dimensional Changes of Garments after Home Laundering