The thickness of paper: What does GSM mean in terms of paper?

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How heavy are your paper stocks? We in the print industry talk all the time about GSM. It’s how we communicate the weight of paper stocks, but what does GSM mean? In this article, we’ll describe what GSM means, and what effect it has on your finished product.

We will also show you how you can choose the correct GSM paper so your project is cost-effective as well as how to avoid some common pitfalls.

What does GSM mean?

GSM stands for Grams per Square Metre and is used for measuring paper weights. It’s often referred to as the thickness of paper but this is not strictly true. While the GSM has an impact on the paper thickness (caliper) of the paper, paper thickness is measured in Microns (or 1000th of a mm). More on this later.

Measuring paper weight requires a very sensitive scale and a means of cutting a pre-determined paper size with a punch, most good paper merchants will have one.

What is GSM in paper weight?

Print buyers use the term GSM to specify the weight of material in a printed product and it is important to get the right weight of paper for a whole range of reasons (some are detailed below). It is worth noting that different paper stocks may feel thinner or thicker even though they are the same weight so it is important to know your thin paper from your thicker paper stocks. As well as your coated from uncoated paper and your double from your triple coated, sounds confusing doesn’t it?

Does the weight of the paper really matter?

GSM is specified on a print project for a host of reasons but most commonly its to do with the feel of the paper. Thicker material is often associated with better quality (rightly so in our opinion). Another reason is to do with postage costs and production and a lower GSM paper will be used to keep an item under the target weight.

Factors for choosing the right paperweights

Here are some things to consider when specifying paper weights.

Cost/Pricing

As a rule of thumb, the higher the GSM, the more expensive the price but not just because the material costs more. Heavier paper usually runs slower through the printing process and weights above 200 GSM can be prone to cracking if they are to be folded, so additional processes such as laminating and creasing are required.

Folding

As mentioned above, heavier materials require creasing to avoid cracking when folded, and some stocks just don’t look good, for instance, brochure covers in 450 GSM paper will tend to spring open instead of lying flat when closed.

Postage

If your brochure is intended to be mailed out, it’s especially important to understand the paper weight so you can estimate the overall weight and how this affects the postage cost. Below is a simple formula for calculating the weight of each page (remember a page is each side of a leaf).

((Page Height in m x Width in m) x GSM/2) x pages of that GSM) this needs repeating for covers which may have different paper stocks and adding to get the total weight.

EG a 24pp A4 brochure with a 250 GSM paper cover and 130 GSM paper text would look like this:

Text – ((.297 x .210 x 130/2) x 20) = 81g Cover ((.297 x .210 x 250/2) x 4) = 31g, therefore 81g + 31g = total weight of 112 g.

Understanding paper thicknesses and weight in practice

Paper coatings (Silk/Gloss/Matt) add weight to the paper but not much thickness, therefore Gram for Gram, Uncoated papers tend to be thicker – to explain here is our GSM paper guide to help you see the difference between thickness and different GSM on Essential Silk (Coated) and Coral offset (Uncoated).

Paper WeightPaper Thickness (Microns)
GSM/GrammageEssential SilkCoral Offset
80n/a96
9080108
10086119
115100n/a
120n/a142
130111n/a
140n/a164
150131n/a
170153196
190n/a218
200181n/a
225210n/a
250239287
300299345
350358407
400421n/a

This video by paper makers Holmen explains really nicely how paper bulk can differ.

GSM paperweights in the real world

Here are some popular paper weights

Business cards

400-450 GSM is the normal paper weight, this gives a nice stiff feel and in my opinion, it conveys quality. Believe me, when it comes to creating the right impression with your business card, the difference between 300 and 400 GSM will make all the difference.

Leaflets and flyers

When printing flyers, it’s not unusual to print on a paper GSM range of 90 GSM and 170 GSM paper and really depends on the target audience and value of the end product. For flyers (we define this as the leaflets unfolded cousin) a slightly thicker stock of 200-300 GSM is often used.

Posters

Posters are usually in place and left alone so a factor to consider is how much contact they will have with passers-by and the elements we typically recommend 150-200 GSM paper for posters but if they are to be outdoors a waterproof alternative is better.

The print size also matters, for instance, large movie posters may need to be a heavier material so they are easier to install.

Brochures

When it comes to brochures, the range is as wide as it is for leaflets, but the most popular paper weights on brochures have a combined weight of around 250 – 350 GSM, meaning a text page would be 150 – 170 GSM with the brochure covers being slightly heavier at 200 – 300 GSM.

It is worth considering the paper sizes here, smaller items can feel very stiff on heavy paper, so speak to your printer about how you want the end product to look and feel.

If your print would be better defined as a booklet or magazine, it will often be printed on much lighter paper although magazine covers still tend to be heavier than the text.

Catalogues

Printed materials such as price lists, catalogues and paperback books are often printed on very thin paper because they are usually printed in very large quantities so are printed on web presses unable to cope with heavier stocks.

Letterhead & compliment slips

Paper weight for stationery items ranges from 80 GSM paper (like copy paper or household printer paper) to a more luxurious feeling 120 GSM paper.

Most of the letterheads and comp slips produced at Smart Printing Company are 100-120 GSM.

Paper stocks are just as important here, often brands select speciality papers with textures and watermarks.

Other printed paper products…

The list is endless, if you have any questions please get in touch, we are happy to advise on the different GSMs and paper types for your printing needs.

What’s the difference between thickness and GSM and what does caliper mean?

Where GSM refers to grams per square metre (a measure of weight) paper thickness is measured in Microns (referred to as caliper) both measures will give you an idea of how the finished printed paper product will feel. They are very different, for example, a premium uncoated paper such as Coral offset weighing 350 GSM with a caliper of 358 microns while a lower grade packaging board of similar thickness could weigh as little as 280 GSM.

Measuring the thickness of paper with a caliper

The reason is that the pulp in the board is denser in the better quality stock which increases the weight more than the thickness, whereas cheaper grades may be “bulky” so the opposite is true.

Conclusion

While there are cost and production considerations when specifying GSM paper weight, the main thing is to understand what you want from the project, how should it feel? How will it be delivered? Then speak to your print provider who should advise you on the impact on production and associated costs. Most things are possible but all carry a price tag so seek advice early. If you want to chat GSM, paper caliper or anything print, please get in touch.

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