Paper GSM & Thickness
Created on 04.27
What is GSM?
GSM — Grams per Square Metre, it is the foundational metric of the paper industry. It measures the weight of one square metre of paper; the higher the number, the heavier and generally thicker the sheet. Whether you're sourcing print collateral, designing packaging, or publishing a book, GSM is always the first specification on the table.
But higher GSM doesn't always mean thicker paper and two sheets at the same weight can feel entirely different.
Many people equate GSM directly with physical thickness, this is one of the most widespread misconceptions in print procurement. Actual thickness is also governed by:
1. Fibre Structure & Raw Material. Long-fibre pulp (such as softwood pulp) is more voluminous than short-fibre pulp, and tends to produce thicker sheets at the same GSM. Recycled paper fibres are shorter and therefore have a relatively higher density.
2. Calendering & Coating- Coated art paper undergoes surface coating and calendering, resulting in high density and a smooth feel and making it significantly thinner than offset paper at the same GSM.
3. Fillers & Additives: Inorganic fillers such as calcium carbonate and kaolin increase paper weight without adding thickness, which is why some high-GSM papers can have a surprisingly low caliper.
4. Bulk / Volume: Bulk / Volume Bulk = Caliper ÷ GSM. It is the professional metric for measuring a paper's "fluffiness." High-bulk papers (such as lightweight book paper) are noticeably thicker at the same GSM
Understanding GSM vs thickness is not just technical but directly impacts your product:
For Packaging:
Box rigidity depends more on thickness and bulk, not just GSM
Choosing the wrong spec can lead to weak structure or unnecessary cost
For Printing
Thickness affects:
Feeding performance
Ink absorption
Color consistency
After years in paper I think that the best paper choice is rarely about numbers alone, but also about how the paper performs in your actual use. What's your ideas?
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