What is GSM in Fabric

Whether you are a newcomer to textile and apparel manufacturing, or a designer, fashion entrepreneur, garment industry professional, apparel merchandiser, apparel retailer or a fabric sourcing guy, and you need to deal with fabric and fabric purchase, you must learn about the fabric GSM. All the things you need to know about the fabric GSM, its application, its effects on the fabric properties, the relation of the fabric gsm and fabric consumption, fabric costing will be discussed in this post.

What does fabric GSM mean?

Full form of GSM is grams per square meter (grams/m2). Fabric GSM represents its weight in grams. GSM is a metric measurement unit of surface or areal density which is used for measuring the thickness of sheet material. Fabric and paper thickness are measured in gsm. For an example, 180 gsm t-shirt means the weight of the knitted cotton fabric used for making that t-shirt is 180 grams per square meter area.

The openness of a fabric is understood by the gsm value. The weight of the fabric is also measured in ounce per square yards, which is a non-metric measuring unit of fabric weight. Denim fabric weight is measured in an ounce.

All about fabric GSM

Fabric GSM Vs Fabric thickness

GSM is one of the primary fabric quality parameters. When you need to purchase a fabric or need to get the fabric development done, you must mention your fabric gsm requirement. The thickness of the fabric depends of the yarn thickness (yarn count), and density of the yarns in the woven fabric. Another way by using thicker yarns, fabric thickness can be increased. This will increase the fabric weight of unit surface area. Fabric fall, stiffness, texture, hand feel and shade depth effect by the fabric weight (GSM).

If you select a lower gsm fabric, you will get a lighter and thinner fabric. The openness of the fabric increases with the reduction of its gsm. We prefer the clothes made of lighter fabrics in the summer and in winter we prefer wearing clothes made of the thicker fabrics for warm. A sweatshirt, fleece jackets are made of higher gsm fabrics (200-300 gsm). So, if you are doing a project on making your own garment, you need to choose the gsm according to the end use of the garment.

After the washing of fabric or garment, fabric gsm increases due to shrinkage of the fabric length and width.

Fabric GSM vs Fabric consumption for a garment and garment costing

To make a garment you need certain yards of fabric. To be more specific, you need a fixed area of fabric sheet whether it is a knitted fabric or woven fabric. This area is the fabric consumption of the garment. Whether the GSM of the fabric increased or decreased, you need the same length of fabric (for a fixed fabric width).

If you take a woven fabric, the unit of measure is in meters (or yards). Let's say you want to make a woven shirt. For that you need 2 meters of fabric of 46 inches width. The GSM of the fabric is let say 160 gsm. If the fabric gsm is increased, the weight of fabric required for a garment (2 meters in length) will increase. Which in turn increase the requirement of yarns and cotton per shirt. So, the cost of the fabric consumed per garment will increase accordingly. 

In a knitted garment, the unit of measure for fabric consumption is grams. You need a certain length of fabric for a knitted garment too. Therefore, if the gsm of single jersey fabric increases, fabric consumption will also increase and vice versa. So, the garment cost will change accordingly.

Fabric selection and Fabric GSM

The selection of fabric GSM depends on the end use of the garment to be made and target costing. If you want to keep a t-shirt price low, you need to cut down the cost in fabric and one way of doing that is reduce the fabric weight (gsm). For making a knitted t-shirt, you can used fabric having gsm range between 120 to 180 gsm and for making a fleece jacket you can pick gsm between 200 to 300 gsm.

Here is an example of fabrics of different weights.
  • Lightweight fabrics: chiffon, linen, organza, cheesecloth, lace, voile, mesh
  • Medium weight fabrics: face towels, hand towels, bath towels, pool towels, sateen, oxford, velvet, taffeta, charmeuse
  • Heavy weight fabrics: Face towels, hand towels, bath towels, pool towels, upholstery fabric, canvas, brocade, poplin, denim
Lightweight fabrics are mostly used in the manufacturing of summer clothes and underwear, while heavy weight, dense materials are popularly used for upholstery and furnishing.

Calculate fabric GSM by using the testing instrument (GSM cutter and weighing balance)

The standard method of measuring fabric GSM is using the calibrated GSM testing equipment. For testing or measuring the fabric weight, one needs a
  1. circular gsm cutter which will cut an area of fabric 1/100 of a square meter (100 cm2). Hydraulic gsm cutter is also available for cutting circular gsm sample.
  2. one digital weighing balance and
  3. fabric sample cutting pad. 
The process involved, cutting fabric specimens using the gsm cutter, weighing those specimens using the digital weighing balance and then measuring each specimen and recording the reading. After the recording of weights, calculate the average weight of each sample.

If you are doing gsm measurement for your fabric, take the fabric specimen from the different part of the fabric roll across the roll length and different places width wise. When you collect the sample from different places, it will give you a better accurate gsm of the fabric. In the opening length of a roll, the fabric might get stretched which will give less gsm value.

You can purchase GSM cutter and equipment from Amazon store.

The gsm measurement of a given fabric sample can be done without the gsm cutter. You need a weighing scale, a marker, and a scissor. For this, cut 10/10 cm fabric test specimen and take the weight of these samples using a digital weighing balance. Consider reading weight for 5-10 samples. To be noted that by using this method you may not get an accurate weight.

Calculate fabric GSM using a formula and fabric construction

In absence of the GSM testing equipment, you can estimate approximate fabric GSM of the fabric sample from the fabric construction. To calculate the fabric GSM from the fabric construction a formula is used by many fabric professionals. I learned this from one of my friends working in a testing lab for more than 13 years.

The fabric gsm calculation formula is:
Fabric GSM = (EPI/warp count + PPI/Weft count) x (100+crimp %) X 0.2327
This formula is applicable for woven fabric GSM calculation. To use this formula, you need the following technical information.
  • Fabric yarn count - warp count as well as weft yarn count 
  • warp and weft density - End per inch (EPI) and picks per inch (PPI) 
  • warp and weft crimp percentage 
Let's find fabric GSM of a fabric sample, which is made of the construction of a fabric is 40 X40 /120 X 60 and warp and weft crimp is 6%. In this fabric construction, yarn count is 40’s and EPI is 120 and PPI is 60. Therefore, gsm of this fabric will be,

Fabric GSM = (120/40 + 60/40) X (100+6%) X 0.2327
Fabric GSM =104.77

The above technical data of a fabric is not easily available. You need to find fabric EPI, PPI and crimp percentage, which takes a longer time. Additionally, there is a question of accuracy level when you measure fabric GSM from fabric construction and using one of these formulas.

Note: In case different counts of warp or weft yarns is used then this formula will not give you correct weight. It is also known as conversion formula from fabric construction to fabric weight.
Another formula for calculating fabric woven gsm from its construction. In the formula, the multiplying factory is a little bit different. It is 23.5. This formula can be used, if warp and weft crimp percentage are different. I found others to use this formula with different multiplying factors.
Fabric GSM= ((EPI/warp count X 1.1) + (PPI/weft count x 1.04)) x 23.5
Where 1.1 and 1.04 are warp and weft crimp factors respectively. Let’s calculate fabric gsm of the above fabric sample using this formula. Assume, in the calculation, we are considering fabric crimp% - 1.1 for warp yarns and 1.04 for the weft yarn.

Fabric gsm= ((120 / (40*1.10)) + (60/ (40*1.04))) x 23.5 = 92.44 grams

GSM Testing Report

In the mass garment manufacturing environment, fabric GSM testing is done during fabric development stage or fabric sourcing stage by the garment manufacturer. Though the gsm is approved at the fabric development, the factory needs to test the bulk production fabric.

Fabric GSM can be measured in in-house by using basic testing equipment which is explained above. Whether you are a fabric manufacturer or a garment manufacturer, you need to provide a fabric test report to your buyer. Fabric GSM is one component of the fabric test report. Though by using in-house gsm testing data, you can ensure that you are using correct fabric, the buyer would not accept it. You need a signed test report from a reputed or a buyer approved testing lab.

As a standard practice, to get the fabric gsm test report, garment manufacturers send the fabric sample from the bulk fabric lot to a testing lab. The testing lab tests the fabric weight using your fabric sample and prepare the testing report. The testing lab maintain standard atmosphere while testing is performed. If the fabric test shows the sample fabric GSM out of tolerance, fabric might be rejected by the garment manufacturer as well as the apparel brands. If the fabric bulk fabric got rejected that is a huge loss for both the fabric manufacturer as well as the garment manufacturer.

Prasanta Sarkar

Prasanta Sarkar is a textile engineer and a postgraduate in fashion technology from NIFT, New Delhi, India. He has authored 6 books in the field of garment manufacturing technology, garment business setup, and industrial engineering. He loves writing how-to guide articles in the fashion industry niche. He has been working in the apparel manufacturing industry since 2006. He has visited garment factories in many countries and implemented process improvement projects in numerous garment units in different continents including Asia, Europe, and South Africa. He is the founder and editor of the Online Clothing Study Blog.

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