GSM and PT Unit Systems: What Is the Difference?
One aspect of packaging that has not been fully researched is its thickness.
The thickness of your packaging can influence its durability, protective properties and aesthetic appeal.
Understanding the weight of packages and the various issues to be considered can help you create packaging that meets your product requirements.
In this article, we will examine some of the important terms used to describe packaging, the unit systems used, how to convert and compare units of weight, and the effect this has on your overall packaging.
We will begin with some definitions to help you understand how to determine the appropriate cardboard thickness for packaging.
What are the GSM and PT units?
Firstly, the most frequently used terms in the context of packaging are PT and GSM, so let's take a closer look at them.
PT is an abbreviation of 'point' and GSM is an abbreviation of 'grams per square metre'.
When considering GSM vs PT, these two terms are used to measure the amount of packaging stock required to make custom packaging to suit your product's needs.
Another measurement you may come across is the weight of the paper in pounds.
This is calculated by taking one ream (i.e. 500 sheets) before it is cut.
These are the fundamental units used in packaging stock.
We will now consider each of these units separately to help distinguish between GSM and PT.
The point system (PT)
As previously mentioned, points are used to illustrate the thickness of a sheet of paper, including corrugated packaging paper.
Calipers are used to measure the thickness, with every point equalling 1/1000th of an inch.
When looking through packaging options, you will notice that many refer to the point system to describe thickness, including 8-point and 16-point options.
You can determine the thickness of the stock by taking a measurement, which will give you a more accurate idea of the protection it will provide.
The higher the PT, the thicker the stock.
Grams per square metre (GSM)
The GSM is the metric equivalent of the point system, since it uses centimetres and metres as its primary units of measurement.
It can be confusing because there is no straightforward way to convert measurements between the two systems.
This is because GSM considers the weight, length and breadth of the paper, as opposed to thickness and height.
Remember that certain packaging materials may appear thick, but this does not necessarily mean they are heavier.
For example, in the case of corrugated packaging, you can have a corrugated fibreboard that feels thicker, but this does not mean it is heavier.
However, the greater the GSM, the thicker and heavier the paper will be.
As a rule, higher GSM paper is of a higher quality because it is more durable and produces better print quality.
So, what is the importance of the GSM unit system?
GSM is important because it is the system that is usually used, making it easier to communicate with vendors who use it.
As well as being easy to use, GSM is significant because it carries more information.
It takes paper weight into account, which is a major consideration when it comes to packaging materials and expenses.
It is also a more accurate way of measuring packaging thickness, making the design process simpler and introducing less confusion to the packaging process.
What are some of the typical measurements you would encounter when considering GSM?
Learn about common GSM paper thicknesses
Knowing the standard measurements of GSM paper will help you make decisions.
Depending on the appearance and feel you want for your packaging, as well as how durable it needs to be, you can decide on the appropriate thickness and weight.
| 35-55 gsm: This is the weight of paper most commonly used for printing newspapers. |
| 90–100 gsm: This is standard printer/copier paper. Bond paper, for example, would be around 110–120 g/m². |
| 120-140 g/m²: Flyers and posters are likely to be printed on this paper, as it is stronger and can withstand wear and tear. |
| 210-300 g/m²: You have touched and felt glossy brochures before, so you will be familiar with this type of paper. |
| 350-400 g/m²: This paper is primarily used for packaging and business cards. |
Once you know the GSM you want to use, you can start using the point system as required. Here's how
Transformation between the GSM and PT unit systems
Since GSM is simply the metric form of the PT system, it can be applied to calculations involving thickness. However, GSM considers weight, so they cannot be used interchangeably.
The following conversion charts can be used to convert between the two systems when considering paper in PT vs. GSM.
Having the correct conversions to hand during the design process can be useful, depending on what your packaging vendor is dealing with, so it is a good idea to provide as much information as possible.
| Thickness / Packaging Material | Weight |
| 13 point Pulp | 200 gsm |
| 14 point Uncoated | 270 gsm |
| 16 point C2S / Solid Bleached Sulfate (SBS)* | 350 gsm |
| 18 point C2S | 400 gsm |
| 24 point Uncoated | 405 gsm |
| 24 point C2S / Solid Bleached Sulfate (SBS)* | 460 gsm |
| 40 point Cotton | 600 gsm |
As you can see, greater thickness does not necessarily equate to greater weight. For example, a 17-point uncoated surface packaging material weighs 350 g/m², whereas the heavier 18-point brown kraft weighs 315 g/m².
Other materials besides paper are used for packaging, including corrugated board. There are many types of corrugated board, including single face, single wall, double wall and triple wall, and they all come in different gsm.
We will use this concept to discuss comparisons of paper weights and thicknesses.
Comparing paper weights and thicknesses
Although the systems used in the US and the metric system can be confusing, the main thing to remember is that the GSM system uses weight as part of its paper measurement.
Knowing the weight and thickness of your packaging material is especially useful when determining the thickness of corrugated paper and cardboard.
These measurements can help you select the most appropriate packing thickness to provide your customers with an excellent unboxing experience while ensuring that your products are strong enough to withstand long-distance transportation and shipping.
Consulting packaging specialists can provide insight into the advantages and disadvantages of various weights and thicknesses, as well as their impact on packaging material costs and shipping expenses.
We will now consider what these various measurements mean for your packaging.
The packaging implications
Now that you have seen the various methods of measuring weight and thickness, how can you apply this knowledge to your packaging materials?
Firstly, distinguish between packaging materials when designing the package, and examine materials objectively.
The thickness of the paper in terms of pt or GSM will help you decide on the best package for your product, ensuring it reaches customers in its original form.
Another important purpose of these measurements is to give you an idea of what the final packaging product will look and feel like.
Would you prefer it to be heavy and dense or light and airy when handed to customers?
Are you going to print images or logos on the packaging? A higher GSM may be required to print images in better quality due to the surface texture.
You also need to decide how you want your packaging to be finished. Would you prefer a matte or glossy finish? This depends on the GSM of your packaging material.
The GSM unit system enables you to collaborate with design professionals to create packaging that truly reflects your brand.
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