GSM — grams per square metre — is the weight of one square metre of paper. Heavier generally means thicker, stiffer and more opaque, but the relationship is not linear, and the paper type matters as much as the number.
The chart we use every day
| Use | Typical spec | Notes |
|---|---|---|
| Novel / text interior | 70–120 gsm offset | Uncoated, easy to read, lightweight for high page counts |
| Full-colour picture book interior | 128–157 gsm art paper | Coated both sides; holds vibrant colour |
| Board book page | 350 gsm C1S mounted to greyboard | Two sheets + core ≈ 1 mm per page |
| Book cover | 250–350 gsm art paper + lamination | Lamination is what makes it durable, not the weight |
| Playing cards | 300 gsm blue-core | Opaque core; hides the face through the back |
| Premium cards | 350 gsm black-core | Denser feel, less warping over time |
| Folding carton | 300–400 gsm C1S or greyboard | Structure and print surface are separate decisions |
| Rigid box wall | 1–3 mm greyboard, wrapped | Wrapped in printed paper; the board is the structure |
| Notebook cover | 250–300 gsm + lamination, or PU | Hardcover planners pair board with a wrap |
| Bible paper | 28–45 gsm | Ultra-thin, opaque; for very high page counts |
Coated or uncoated
Coated (art paper, C1S, C2S) has a clay surface that holds ink sharply and produces richer colour. Uncoated (offset, kraft) is more absorbent, feels more natural, and — critically for workbooks and planners — you can write on it.
C1S versus C2S
C1S is coated on one side only; C2S is coated both sides. C1S exists for products where one face is printed and the other is glued, mounted or left raw — board book pages, rigid box wraps, and puzzle sheets all use it. C2S is for anything printed both sides, like a card face and back or an illustrated spread.
Two questions that decide the spec
- Will it be written on? If yes, uncoated — and generally 80–100 gsm for comfortable pen feel
- Will it be handled hard? If yes, the lamination and the binding matter more than adding 50 gsm
Stocks vary by market, so it is worth confirming availability before finalising a spec that depends on a specific weight. We keep a paper sample book with every stock and weight we run, labelled and tactile — request one free and you can compare the actual papers rather than guessing from a chart.