GSM (grams per square meter) is a very important concept in the textile and garment industry. It shows the weight of fabric in one square meter. A fabric with a higher GSM is heavier and usually thicker, while a fabric with a lower GSM is lighter and usually thinner. For woven garment merchandisers, understanding how to calculate GSM is essential. It helps confirm whether the fabric ordered from the supplier matches the buyer’s required specification. Although suppliers usually provide the GSM value, merchandisers should still know how to check and calculate it correctly.
What is GSM?
GSM stands for grams per square meter. It is the metric unit used to measure fabric weight. The unit is written as g/m² or gm/m².
In simple terms:
- High GSM = heavier fabric
- Low GSM = lighter fabric
This measurement is widely used in fabric development, costing, sourcing, and quality control.
What is Crimp Factor?
Crimp factor refers to the waviness or bending of yarn inside the woven fabric structure. Because yarn in woven fabric is not perfectly straight, its actual length in the cloth is longer than the straight distance between its two ends. Crimp percentage or crimp factor is defined as the difference between the straightened yarn length and the length of the yarn as it lies in the fabric, expressed as a percentage or factor. This is important because more crimp means more yarn is used in the fabric, which affects fabric weight and GSM.
GSM Calculation Method for Woven Fabric
To calculate the GSM of woven fabric from fabric construction, the standard formula is: GSM = [(EPI / Warp count × Warp crimp factor) + (PPI / Weft count × Weft crimp factor)] × 23.5
Meaning of the terms:
- EPI = Ends per inch
- PPI = Picks per inch
- Warp count = yarn count in the warp direction
- Weft count = yarn count in the weft direction
- Warp crimp factor = crimp factor of warp yarn
- Weft crimp factor = crimp factor of weft yarn
- 23.5 = conversion constant used in the formula
Example:
Suppose the woven fabric construction is as follows:
- Warp count = 50
- Weft count = 40
- EPI = 130
- PPI = 60
- Warp crimp factor = 1.2
- Weft crimp factor = 1.0
Step 1: Calculate warp contribution – (130 / 50) × 1.2 = 3.12
Step 2: Calculate weft contribution – (60 / 40) × 1.0 = 1.5
Step 3: Add both parts and multiply by 23.5 – GSM = (3.12 + 1.5) × 23.5!! GSM = 4.62 × 23.5!!! GSM = 108.57
Important Point:
Warp and weft must be calculated separately. They should not be combined into one single fraction. Each direction contributes independently to the total fabric weight, so the formula must be followed step by step.
Practical Note:
This formula gives the theoretical GSM based on fabric construction. However, actual GSM in production may still vary because of other factors such as:
- fiber type
- yarn twist
- finishing process
- moisture content
- fabric relaxation
So, in actual factory practice:
- use the formula for estimation and planning
- use physical testing, such as a GSM cutter, for final quality confirmation
Conclusion / Final Words
GSM is one of the most important fabric parameters in the textile sector. A woven garment merchandiser should clearly understand both the meaning of GSM and the calculation method. By using the correct formula and understanding the role of crimp factor, it becomes easier to estimate fabric weight and check whether the supplied fabric meets the buyer’s requirement.
At the same time, it is important to remember that calculated GSM is only a theoretical value. For real quality control, actual fabric testing is still necessary.
