A child writes a spelling list in a light exercise book. Turn the page over, and the words from the front show through, faint but clearly readable. The paper is not damaged. It is simply light. This is a GSM problem, and it is one of the most common reasons families ask why a book "feels cheap" when the ruling and size were exactly what the booklist asked for.

This guide explains what GSM means, why lighter paper is more likely to show through or bleed, and how to choose the right weight for school writing and printing. It is part of our notebooks and paper for school guide.

Quick answer

GSM stands for grams per square metre. It is how paper weight is measured. A higher GSM number means a heavier sheet, though not always a thicker one, since fibre density and coating also affect feel. Lighter paper, such as 70gsm, is more likely to show ink or pen through the back of the page, especially with pens that use wetter ink. For school printing, 80gsm is the common standard. For handwriting on both sides of a page, or for pens and markers that bleed easily, a heavier sheet reduces show-through.

What GSM Actually Measures

GSM stands for grams per square metre. It is calculated by weighing a one square metre sheet of the paper in question. A paper rated at 80gsm weighs 80 grams per square metre, regardless of the sheet's actual size once cut down for a notebook or a ream.

GSM measures weight, not thickness. Two sheets with the same GSM can still feel different, because fibre density, bulk and any coating also change how thick a sheet feels in the hand. This is a widely used industry explanation, and it holds true whether the paper is destined for a school exercise book or a printed flyer.

Key note: A higher GSM number is a reasonable guide to thickness within the same paper type and brand, but it is not an exact measurement of thickness on its own. If you need an exact figure, some manufacturers publish a separate thickness or calliper measurement alongside the GSM rating on their spec sheets.

Why GSM Affects Show-Through and Bleed

Show-through and bleed are related but slightly different problems.

• Show-through happens when writing or printing on one side of a page becomes visible from the other side, without the ink actually soaking through the fibres.
• Bleed-through happens when ink physically soaks through the paper and becomes visible, sometimes even smudging on the reverse page.

Lighter paper is generally more prone to both, although the actual result also depends on the paper's fibre, coating and the type of ink used. Paper in the 70–80gsm range is widely used for everyday printing, but wetter inks can be more likely to show through on lighter sheets. Heavier paper can reduce show-through, although the result also depends on paper construction and ink type. 

The paper's thickness is one factor. Absorbency, fibre quality and coating matter too. Thin, uncoated paper with loosely packed fibres will show through more than a denser sheet at the same GSM.

Common School Paper Weights Compared

Here is how the common weights compare for school use.

Our 80gsm vs 100gsm copy paper guide goes deeper into when the heavier ream is worth the extra cost for printing specifically.

Why Some 70gsm Paper Bleeds and Some Doesn't

This is where GSM alone does not tell the whole story. Two 70gsm reams from different manufacturers can behave differently under the same pen.

Factors beyond the GSM number include:

• Fibre quality: Long-fibre pulp tends to hold up better than paper padded with fillers.
• Coating: Some papers include treatments that reduce ink absorption, even at a lower weight.
• Ink type: Wetter inks, such as those in some gel pens and fountain pens, deposit more liquid and are more likely to soak through than a dry ballpoint.
• Printer type: Inkjet printers lay down wet ink and are more likely to show bleed-through on thin paper than laser printers, which fuse dry toner onto the page.

Key note: If a particular 70gsm ream bleeds badly with your child's usual pen, a different 70gsm brand may perform better. GSM is a useful shorthand, but it is not the only variable.

GSM in Exercise Books vs Copy Paper

Exercise books and copy paper are often held to different weight expectations, because they are used differently.

Exercise books are commonly made from lighter paper, in the 55gsm to 80gsm range, since students usually write on one side per page and the book is bound to stay closed. Copy paper is typically heavier on average, because it is printed on more intensively and often used double-sided.

This does not mean exercise book paper is lower quality. It means the weight is matched to expected use. A student using a fountain pen or a heavy gel pen in a light exercise book may still notice more show-through than the same pen would cause on 80gsm copy paper.

If your child's exercise books show through more than expected, check whether the pen is the actual cause before assuming the paper is at fault. Our guide on ruling and format choices for exercise books can help you match the right book to the right subject and stage.

Matching Paper Weight to the Pen

Pen choice interacts with GSM more than most people expect.

A quick test helps before committing to a full order. Write a few lines with the actual pen your child uses on the back of a sample page. If the writing shows through clearly, either move to a heavier paper or accept some show-through as normal for that pen and paper combination.

GSM and Printer Compatibility

For home printing, GSM matters for two reasons: show-through on double-sided pages and whether the printer can handle the paper correctly. Many home inkjet and laser printers are designed to handle standard copy paper, but the supported paper weight varies by printer model. Very light or heavy paper may feed differently or require a specific paper tray, so check your printer's manual before using paper outside its recommended range. 

Check your printer's manual for its supported weight range before buying paper for a heavier print job, such as a printed project cover or a double-sided handout. Our guide on why printers keep jamming covers paper-related jam causes beyond weight, including storage and tray habits.

If you print regularly at home, it is worth keeping two paper weights on hand rather than one. An 80gsm ream covers everyday worksheets, reading logs and general printing. A smaller stock of 100gsm suits the occasional project cover, certificate or double-sided colour page where show-through would look untidy. This avoids paying a premium for heavier paper on every print job, while still having the right option available when it matters. Buying in a standard ream size also makes it easier to compare weight against price across brands, since reams are usually sold in the same 500-sheet count regardless of GSM.

Paper Options by GSM at School Stationery Supplies 

The products below are listed in our Notebooks & Paper collection. Weight details come from the live product pages. Always confirm current specifications before ordering.

If your child's pen tends to bleed through lighter paper, pairing it with an 80gsm option for printed work and testing the pen directly on exercise book paper before a bulk order, avoids most surprises.

Common Mistakes When Buying by Paper Weight

• Assuming all 70gsm paper behaves the same: Brand, fibre quality and coating all affect show-through at the same GSM.
• Blaming the paper when the pen is the real cause: Test the actual pen before switching paper weights.
• Buying the lightest paper to save money for double-sided printing: This is the most common cause of frustrating bleed-through.
• Ignoring the printer's supported weight range: Very light or very heavy paper can cause feed issues.
• Confusing GSM with thickness: A higher GSM is a useful guide, but coating and fibre density change how thick a sheet actually feels.

Frequently Asked Questions

What does GSM mean on paper?

GSM stands for grams per square metre. It measures how much a one square metre sheet of the paper weighs, and is the standard way paper weight is described in Australia and most other countries.

Why does 70gsm paper bleed more than 80gsm?

Lighter paper has less fibre to absorb ink, so wetter inks are more likely to soak through and become visible on the other side. This effect is stronger with gel pens, felt tips and fountain pens than with pencil or ballpoint.

Is higher GSM always better for school paper?

Not always. Heavier paper reduces show-through and bleed but costs more and adds weight to a school bag. For most everyday writing and printing, 80gsm strikes a reasonable balance.

What GSM should school exercise books be?

There is no single fixed standard. Many exercise books sit in the 55gsm to 80gsm range. The right weight depends on the pen used and how much show-through is acceptable for that subject.

Does GSM affect how a printer handles the paper?

Yes. Very light paper can feed unevenly through some printers, and very heavy paper may need a manual feed tray or may exceed the printer's supported range. Check your printer's manual before buying unusually light or heavy paper.

Choosing the Right Paper Weight With Confidence

GSM is a simple number with a real effect on how school paper performs. Lighter paper, including much of the 70gsm range, is more likely to show ink through the back of the page, especially with wetter pens. Heavier paper can reduce show-through and is often useful for double-sided printing, although the best choice depends on the paper construction, printer and ink or toner being used. 

Test your child's actual pen on a sample page before committing to a full order, and match the paper weight to how it will actually be used. For a wider look at exercise books, notebooks and copy paper together, see our notebooks and paper for school guide. Ready to shop paper by weight? Browse our Notebooks & Paper collection.

Supporting Articles in This Series

• Notebooks & Paper for School: The Complete Australian Buying Guide
• Dotted Thirds, 8mm, 14mm: Australian Exercise Book Rulings Explained
• A4 vs A5 Exercise Books: Which Size Does Your Child Actually Need?
• How Many Exercise Books Does a Student Need Per Year?
• Stapled vs Spiral vs Wiro-Bound: Which Notebook Binding Lasts a Year?
• How to Cover School Books Without Bubbles (Contact vs Slip-On)
• 80gsm vs 100gsm Copy Paper: When the Heavier Ream Is Worth It
• Recycled Notebooks and Copy Paper: Do They Hold Up in the Classroom?
• Ream, Box or Pallet? Bulk Copy Paper Quantities Explained
• Why Your Printer Keeps Jamming (It's Usually the Paper)

About the Author: 

The School Stationery Supplies Team publishes practical buying guides for Australian students, parents and teachers. Visit School Stationery Supplies for notebooks, paper, pens and school essentials.

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