You are ordering T-shirts, and the supplier writes: "single jersey, 100% cotton". At first glance that sounds like enough. But one knitted-fabric mill lists 100% cotton jersey knitted from the same yarn count, 30/1, at both 160 g/m² and 240 g/m². Those are noticeably different fabrics. That is why your order needs a number - and a tolerance next to it.
We are TYX Manufacturing, an OEM and ODM clothing manufacturer with eight factories in China and Cambodia. T-shirts and polos are one of our product categories, and fabric sourcing is one of our services. Below is what is worth knowing about fabric weight before you approve a fabric.
What g/m² (GSM) actually means
Fabric weight - in standards, "mass per unit area", in the trade usually GSM, grams per square metre - tells you how many grams one square metre of fabric weighs. The higher the number, the more material in every square metre.
For knitted fabrics, the measuring method is set out, for example, in the Russian/CIS interstate standard GOST 8845-87 (in Russian). Three specimens of 200 x 200 mm, or six specimens of 100 x 100 mm, are cut from the fabric. All specimens are weighed together, the mass is divided by their total area, and the result is grams per square metre. The test is run under standard atmospheric conditions. The ASTM standard for the same measurement is ASTM D3776: its test methods cover fabric mass per unit area and are applicable to most fabrics.
Under GOST 8845-87, this method is not used on finished garments. Fabric weight is determined by the fabric manufacturer, on the fabric itself. Only when there is a dispute are the values determined on finished garments cut from that fabric.
Same fabric name, different weight
The name of a fabric describes its knit structure, not its weight. Here is what one knitted-fabric mill lists in its catalogue:
- single jersey, 100% cotton: 140-150, 160 and 240 g/m²;
- interlock, 100% cotton: 190-200 and 300 g/m²;
- fleece-back and terry knits (futer) of various compositions: from 230-240 up to 330 g/m².
So "cotton jersey" only describes half of the fabric. Until the weight is named, two suppliers can offer noticeably different fabrics under the same name.
The same catalogue also lists, for each item, how many running metres you get from a kilogram. But running metres also depend on the fabric width. Weight per square metre tells you directly how much fabric area a kilogram gives. One kilogram of 240 g/m² fabric gives about 4.2 square metres; one kilogram of 160 g/m² fabric gives 6.25 square metres.
How far actual weight can drift from the spec
The actual weight of a fabric can differ from the declared one, and the standard explicitly allows for this. Under GOST 28554-2022 for knitted fabrics, the weight may be lower than declared by no more than 6%. The exception is warp-knitted fabrics, where the limit is 5%. The standard sets no limit on the weight being higher than declared.
For example, if your order says 180 g/m², the lower limit under this rule is about 169 g/m².
There is a caveat. GOST 28554-2022 has been in force in Russia since 1 April 2023, but a factory in China is not bound by it. So it is better to write the tolerance directly into your spec sheet or contract rather than assume it is implied.
Why a kitchen scale will not help
You can weigh a swatch at home, but it is usually not accurate enough. A 10 x 10 cm swatch of 160 g/m² fabric weighs only 1.6 grams. If the scale is off by one gram, the result moves by 100 g/m². Even on a 20 x 20 cm swatch, the same error gives 25 g/m².
A reliable check needs a precise scale and a standard method. In production there is incoming inspection: fabric and trims are checked as soon as they arrive, before cutting, and fabric weight is one of the things checked.
What to specify about the fabric in your spec sheet
GOST 28554-2022 recommends stating these characteristics, among others, in a fabric's technical description. They are easy to carry over into the specification for your T-shirts:
- Knit structure: single jersey, interlock, fleece-back and so on.
- Fibre composition in percent.
- Yarn linear density (in tex).
- Fabric weight in g/m² and the permitted deviation in percent.
- Stretch, or stretch group.
In the bill of materials of a tech pack, each fabric is listed with its composition, weight (in g/m² for knits), colour number and supplier, if known. Once the weight and tolerance are written down, a dispute about fabric weight is settled by weighing.
For more on tech packs, see "What Is a Tech Pack and Why Every Clothing Manufacturer Asks for One". To see where fabric and finished garments are checked during production, read "How Quality Control Actually Works at Every Production Stage".
Sources
- GOST 8845-87 "Knitted fabrics and garments. Methods for determination of moisture, mass and surface density" (in Russian)
- GOST 28554-2022 "Knitted fabrics. General specifications" (in Russian)
- ASTM D3776/D3776M "Standard Test Methods for Mass Per Unit Area (Weight) of Fabric"
- Knitted-fabric mill catalogue (in Russian): single jersey, interlock, fleece-back
If you are choosing fabric for T-shirts, send us your spec sheet or a photo of a sample through the inquiry form. We reply within 4 business hours.