The paper GSM guide for book-binders

GSM, short for grams per square metre, is the standard weight measure for paper. A sheet of 100gsm paper weighs 100 grams per square metre regardless of size. For a book-binder, gsm is the single most predictive number on a paper spec sheet — it determines feel, fold, ink behaviour, and whether the finished book lies flat.

How gsm maps to use

| GSM range | Typical use | Behaviour | |---|---|---| | 60–80 | Bibles, dictionaries, newsprint | Folds easily, shows through | | 80–100 | Writing pads, photocopier | Fine for ball-point, shows with fountain pen | | 100–120 | Journals, diaries | Safe default, handles fountain ink | | 120–140 | Mixed-media journals | Takes light washes without cockling | | 140–200 | Sketchbooks | Holds a full wash; heavier to carry | | 200–300 | Watercolour, endpapers | Cockles less; folds crack without scoring | | 300–400 | Covers, cards | Only for single-leaf use |

The fountain-pen threshold

For fountain-pen users in India where humidity is often above 70%, the ghosting threshold sits at 100gsm for uncoated recycled paper and 90gsm for cotton-rag. Below that, ink shows on the reverse. 120gsm is the practical safe default for a daily journal.

Folding vs cracking

Paper above 180gsm cracks when folded without scoring. If you want 200gsm pages in a book, you need to score with a bone folder along the spine fold first. Below 150gsm, a clean finger-crease is enough.

Bulk — how thick will my book be?

Thickness is not just gsm. It also depends on the paper's density (rough cotton-rag is bulkier than smooth offset). A rule of thumb: 96 pages of 120gsm cotton-rag is about 11mm of textblock, while 96 pages of 120gsm smooth offset is about 8mm.

What we stock

Our paper supplies page lists four weights: 100gsm recycled for softcover notebooks, 120gsm mixed-media (the default), 150gsm for sketchbooks, and 250gsm watercolour. Each has its gsm, recycled percentage, and feathering test photographed so you can compare before you order.

Where to go next

To understand how gsm interacts with binding choice, read our binding styles compared post. To try a pre-cut textblock at the right weight, the Japanese stab notebook kit uses 120gsm recycled.

FAQ

What does GSM mean for paper?

GSM stands for grams per square metre. It is the weight of one square metre of a paper, and it is the best single indicator of thickness and ink performance.

What GSM is best for a journal?

120gsm is the safe default for a journal. It holds fountain-pen ink without bleed-through, folds cleanly, and feels substantial without being heavy to carry.

Can I use 80gsm paper for bookbinding?

Yes for a pamphlet or notebook with ball-point pens. Avoid it for fountain-pen or ink-wash journals because it will ghost.

Is higher GSM always better?

No. Above 180gsm paper cracks when folded and the book gets heavy. Choose the gsm that matches the tools you will use on the page.