GSM stands for grams per square metre: the weight of one square metre of fabric. It is the number buyers use for knit fabric and most wovens, while denim and canvas are usually sold by ounces per square yard. Weight alone does not describe a cloth. Two fabrics of 180 GSM can feel, drape and wear quite differently, and the same fabric weighs more after washing than before. This guide covers what the number measures, what moves it, and how to put it in writing so a sample and the bulk order agree.
Garments Hub BD is a sourcing desk in Dhaka; factories on its bench make the goods. An enquiry in a bench category is quoted by two factories and compared on one sheet within 48 hours. A finished weight stated with its tolerance and test is what lets those two quotes be read as like for like.
What GSM measures and how ounces convert
GSM is the mass of one square metre of fabric, weighed after the sample has rested in a standard atmosphere so that moisture does not distort the reading. Ounces per square yard measure the same thing in imperial units. One ounce per square yard equals about 33.9 grams per square metre, so multiply ounces by 33.9 to get GSM, and divide GSM by 33.9 to get ounces. US mills sometimes quote knit fabric in ounces too.
A worked example. A laboratory cuts a disc of 100 square centimetres from the fabric and it weighs 1.8 grams. A square metre holds 100 such discs, so the fabric is 180 GSM, or about 5.3 ounces per square yard. In the other direction, a 12 ounce denim is about 407 GSM.
Some mills quote grams per running metre at a stated width instead. Divide that figure by the usable width in metres to get GSM: 270 grams per running metre at 1.5 metres wide is 180 GSM. Ask which width the mill means, since the full width with selvedges and the cuttable width differ.
Why two fabrics of the same GSM feel different
Weight is the result of the yarn and the construction together. Yarn count (Ne, written as 30s or 20s) says how fine the yarn is, and a higher count is finer. As a typical guide, a 30s single jersey usually lands around 140 to 160 GSM and a 20s single jersey nearer 180 to 200 GSM, but stitch length moves both. A fine yarn knitted tight and a coarse yarn knitted loose can reach the same weight, and the first will feel smoother and denser.
Construction changes hand just as much. Interlock is a double knit, smooth on both faces and firmer than single jersey of the same weight. Pique has an open, textured face that breathes. Fleece is brushed on the back, so it lofts and feels warmer than its weight suggests. In wovens, the number of threads per centimetre and the weave (poplin, twill, canvas) decide whether a given weight feels crisp or soft. Always pair the weight with the yarn and the structure.
Typical fabric weights by garment
The ranges below are typical starting points, not rules. A brand with a heavy, boxy look will sit at the top of a range, and a summer or layering line at the bottom. The garment pages on this site go into each product in more depth.
- T-shirts: usually 140 to 220 GSM single jersey; above 200 GSM reads as a heavyweight tee.
- Hoodies and sweatshirts: usually 240 to 400 GSM in French terry or brushed fleece, with heavyweight styles above that.
- Leggings: usually 180 to 300 GSM in a stretch knit; lighter cloth risks showing through when stretched.
- Chinos and workwear: chino twill usually 200 to 300 GSM; workwear twill and canvas usually 250 to 400 GSM.
- Denim: usually 4 to 8 oz for shirts and dresses, 11 to 14 oz for jeans and jackets.
- Towels and sheets: bath towels usually 450 to 700 GSM terry; sheets are bought by thread count rather than GSM.
How washing, dyeing and finishing move the weight
Fabric off the knitting machine (greige) weighs less than the same fabric after dyeing and finishing, because finishing compacts it. The figure that matters is the finished weight, so write "finished GSM" and never accept a quote for greige weight without knowing it.
Washing moves the number again. When a cotton jersey shrinks, the same mass sits on a smaller area, so GSM rises. A worked example: a 170 GSM jersey that shrinks 5 percent in length and 5 percent in width ends up on about 90 percent of its original area, and weighs about 188 GSM. Garment dyed and washed programmes therefore need two figures in the tech pack: the fabric weight before washing and the target after it. Denim weight is usually stated for the unwashed cloth, and a heavy wash changes it.
How fabric weight drives the price
Knit fabric is usually bought by the kilogram, so the fabric cost of a knit garment rises almost in step with its GSM. A worked example: moving a tee from 150 to 200 GSM puts about a third more fabric by weight into every piece, before any difference in yarn quality. Woven fabric is usually priced by the metre, but a heavier weave still carries more yarn and costs more per metre.
Weight also reaches costs further down the sheet. Heavier garments fill more cartons, which counts for air freight in particular, and heavy fleece takes longer to dry and finish. When two quotes differ, check first that both priced the same finished weight. The guide to how a garment price is built covers the rest of the cost sheet.
Writing weight into the tech pack, and the test behind it
State the finished weight as a number and a unit, with a tolerance. Plus or minus 5 percent is a common tolerance on knit fabric; tighter limits are possible but can mean more rejected rolls. Say at which stage the weight applies: after dyeing and finishing, and, for washed garments, after the garment wash as well.
Name the test. ISO 3801 is written for woven fabric and gives mass per unit length and per unit area. EN 12127 measures mass per unit area from small samples and works for any fabric, knit included. On bulk, ask for a sample from each dye lot to be weighed before cutting, so a light batch is found while it can still be replaced.
What to put in your specification for fabric weight
- Finished weightThe number and unit: GSM for knits and most wovens, ounces per square yard for denim and canvas.
- StageAfter dyeing and finishing, and for washed or garment dyed styles, the target weight after the garment wash too.
- ToleranceA plus or minus figure, commonly 5 percent on knit fabric, so both sides know when a roll fails.
- Yarn and constructionYarn count and spinning, and the structure such as single jersey, interlock, fleece or twill, beside the weight.
- Test methodEN 12127 for any fabric from small samples, or ISO 3801 for woven fabric, named in the tech pack.
- Bulk checkA sample from each dye lot weighed before cutting, with the readings recorded against the stated weight.
Questions buyers ask
Is a heavier GSM a sign of a better garment?
No. A heavier fabric is warmer, more opaque and often more durable, but it is also stiffer and costs more. How the garment wears depends as much on the yarn, the evenness of the knit and how the cloth behaves after washing. A well finished 160 GSM combed jersey can outlast a loosely knitted 200 GSM one.
What GSM tolerance should I accept?
Plus or minus 5 percent is the common tolerance for knit fabric, so a 180 GSM order accepts readings from 171 to 189 GSM. Some buyers set 3 percent on basics where hand feel matters. A tighter limit is reasonable, but it can mean more rejected rolls and a later cutting date if a batch has to be replaced.
Can I check GSM on a finished garment?
Roughly. Cut a disc of known area from a flat, single layer panel of a spare garment, away from seams and prints, weigh it and scale it up to a square metre. Weighing a whole garment does not give GSM, because seams, ribs, labels and trims all add weight.
Should denim weight be stated before or after washing?
Both, if the jeans are washed. Denim is usually sold by its unwashed weight in ounces per square yard, and a garment wash changes the weight and the hand. Put the mill's unwashed weight in the tech pack, then the look and feel you expect after the wash, approved on a washed sample.
Why do two quotes at the same GSM differ in price?
Because weight is only one input. One factory may have priced combed ring spun yarn and the other open end, or a different count, finish or dye. Ask both to state yarn, construction and finished weight on the quote, then compare the fabric line before anything else.
Planning an order?
Send the tech pack or a sketch with quantities. A compared quote in 48 hours on bench categories.