GSM is nothing but the standard unit of measuring the weights of the fabric in terms of Grams per Square Metre.
GSM is a metric measurement of the weight of the fabric.
This measurement is used most commonly to express the weight of fabric but still in some clothing items marked in imperial weights as Oz / square yard(ounces per square Yard).
GSM is a short form of grams per square meter. It is simply how much 1 square meter of fabric weighs.
It gives an idea about the density of the fabric. Higher the Grams per Square Metre denser the fabric and vice a versa. It is also written as gm/sq.meter.
Importance Of GSM
GSM is one of the most important factors to ascertain the quality parameters durability as well as processing requirements of the textile substrate.
Fabric for different end uses/applications is selected based on the grammage of the material.for rigorous/abrasive application fabric with heavy Grams per Square Metre is preferred where as low GSM fabric is preferred for clothing and comfort purpose.
Processing of the fabric also has some interrelation with GSM of fabric. So it is important to calculate the accurate grammage of textile material. So as the end use of the textile material is dependent on GSM it plays very vital role in textile.
As a garment merchandiser and textile technologist, it is important to have knowledge about the methods of calculating GSM.
The weight of the fabric is also expressed in terms of weight per unit length.it is usually referred to the weight per running yard.this usually depends on the width of the fabric. Fabric width usually depends on the working width of the loom.
Earlier, there was another term used for expressing the weight of the fabric or grammage of the fabric that is lbs/ 100 yards. This term was used by British standard. This expression is used equally for woven as well as knitted fabric.
To measure lbs / 100 yards there was a template and quadrant balance. The area of the template is 1/100 square yard of which each arm is 1/10 yards in length.
1) Density Of Warp And Weft In Fabric
It is usual that as the density of warp that is EPI and density of weft that is PPI increases in fabric structure the GSM of the fabric increases because it is obvious that increase of ends or picks will make fabric heavier.
This is one of the most important factors because of the end user, feel, strength and many other specifications of fabric are depend on this factor. In the same way along with density count of warp and weft also matters to the GSM of fabric.
3) Crimp Percentage
Higher the crimp percentage means more the amount of yarn accommodated in the given length so that higher the crimp in warp and weft higher will be the GSM of fabric.
Formula To Calculate GSM-
1) Calculate GSM From The Fabric Construction In Woven Fabric
To calculate the GSM of fabric we must know the various factors of fabric construction such as warp and weft count, crimp percentage of warp and weft, density of warp(EPI) and weft (PPI)
From these factors, by the following formula, It can be derived directly
GSM = ((EPI* warp crimp/warp count)+(PPI*weft crimp/weft count))*23.5
Fabric construction of woven fabric is EPI- 80, PPI – 52, warp count-60, weft count 60, weft crimp percentage is 5.5%, warp crimp percentage 4% the what will be the GSM of fabric?
Answer- for given fabric,
PPI – 52
weft count 60
weft crimp percentage 5.5%
warp crimp percentage 4%
Now by given formula
= ((EPI* warp crimp/warp count)+(PPI*weft crimp/weft count))*23.5
=237.27 grams/ sq.meter
2)By GSM Cutter
GSM cutter is nothing but a fabric gsm checking machine.This method used for woven, nonwoven & knitted in this method cutter and balance is used.
The cutter has a circular cutter and the area of cut fabric swatches is 1/ 100 sq.meter.
About GSM Cutter
In the market, there are the number of manufacturers of cutter but the basic principle is to remain same.
This cutter is provided with the build in 4 knives by revolving the handle knob a quarter of a turn the cutter produces a circular sample of 100 sq.cm which is equal to 1/ 100 sq.meter so just by multiplying the weight by 100 it will give GSM.
The design and precision manufacture of the instrument ensures the specimens are perfectly circular and have smooth edges.
1) cut 5 swatches by the GSM cutter from the different parts of the fabric.
2) avoid the swatches from the selvedge area of the fabric.
3)then weigh one by one those 5 swatches on electronic balance accurately.
4) calculate the average weight of the swatch.
5) then simply by multiplying the average weight by 100 we directly get the actual GSM of fabric.
E.g. weights of 5 swatches are 1.2gm, 1.3gm, 1.5gm, 1.1gm, 1.2 gm respectively.
Average weight of cut swatches=( 1.2+1.3+1.5+.1.1+1.2)/5
Average weight of cut swatches = 1.26 gm
Fabric GSM= average weight of cut swatch *100
By Using GSM Formula
Fabric GSM can be calculated easily even if we don’t have circular GSM cutter. It can be calculated by using following formula.
GSM of fabric= (weight of the sample in gram *10000)/ area of sample in sq.cm
For this, we just need to take the weight of the sample and take the area of the available sample in sq.cm.