Calculating the spine width of a book or booklet
Independent guide, updated on . Practices vary from one workshop to another: have your printer confirm the values.
For a square-back book or booklet (glued or sewn), the cover wraps around a spine whose width you need to know before laying out the cover: that is where the title and the author's name go. A miscalculated spine leaves the title off-centre on the spine or spilling over onto the front or back.
The formula
spine width (mm) = number of inside pages ÷ 2 × thickness of one sheet (mm)
- You divide by 2 because one leaf carries 2 pages (front and back).
- Count the inside pages only, not the 4 cover pages.
- Sheet thickness is often given in micrometres (µm): 1 mm = 1000 µm, so 120 µm = 0.12 mm.
If you only know the grammage
Thickness can be derived from the grammage and the paper's bulk (its volume):
thickness of one sheet (µm) = grammage (g/m²) × bulk (cm³/g)
Example: a 90 g/m² paper with a bulk of 1.5 is 90 × 1.5 = 135 µm thick, i.e. 0.135 mm.
Published thicknesses by grammage
The following values come from one manufacturer's technical data sheets (Arctic Paper). They are target values: the manufacturer states that they may change, and the actual thickness varies by a few percent from one batch to another. They give an order of magnitude; preferably use the data sheet of the paper your printer actually chooses.
| Paper type (product) | 80 g/m² | 90 g/m² | 115 g/m² | 130 g/m² | 150 g/m² | 170 g/m² |
|---|---|---|---|---|---|---|
| Silk coated (Arctic Silk+, bulk ≈ 0.93 to 0.97) | — | — | 107 µm | 125 µm | 145 µm | 165 µm |
| Matt coated (Arctic Matt, bulk ≈ 0.98 to 1.01) | — | — | 113 µm | 129 µm | 150 µm | 172 µm |
| High-bulk matt coated (Arctic Volume White, bulk 1.1) | — | — | 126 µm | 143 µm | 165 µm | 187 µm |
| Uncoated offset (Amber Graphic, bulk ≈ 1.2) | 99 µm | 110 µm | — | — | — | — |
| Bulky book paper (Munken Print Cream 15, bulk 1.5) | 120 µm | 135 µm | — | — | — | — |
For Amber Graphic offset, the data sheet also gives 145 µm at 120 g/m²; for Munken Print Cream 15, 150 µm at 100 g/m².
Important caveat: two papers of the same grammage can have very different thicknesses. A 90 g/m² bulky paper (135 µm) is thicker than a 115 g/m² matt coated paper (113 µm). Never calculate a spine from the grammage alone without knowing the paper type.
Worked examples
| Publication | Inside pages | Paper | Calculation | Spine |
|---|---|---|---|---|
| Novel | 200 | bulky 80 g/m², 120 µm | 200 ÷ 2 × 0.120 | 12.0 mm |
| Essay | 300 | offset 90 g/m², 110 µm | 300 ÷ 2 × 0.110 | 16.5 mm |
| Catalogue | 64 | matt coated 115 g/m², 113 µm | 64 ÷ 2 × 0.113 | 3.6 mm |
| Photo book | 96 | matt coated 150 g/m², 150 µm | 96 ÷ 2 × 0.150 | 7.2 mm |
| Dissertation | 120 | offset 90 g/m², 110 µm | 120 ÷ 2 × 0.110 | 6.6 mm |
What the formula does not tell you
- The cover: with perfect binding, the cover (often 250 to 350 g/m², i.e. a few tenths of a millimetre) is added on each side; some printers include it, others do not. With a hard cover (case binding), the spine is noticeably wider than the book block and has its own construction: only the printer can give you the measurement.
- Ink, glue, sewing and humidity add or remove a little thickness.
- The minimum spine: below a few millimetres, it is hard to print legible text on the spine, and a perfect-bound spine may not hold well. Ask the printer for the minimum width they accept and whether they recommend spine text.
The right method
- Choose the inside paper with the printer and ask for its thickness or bulk.
- Calculate the spine with the formula (or the calculator).
- Ask the printer for the cover template: it shows the exact spine width, the bleed and, where applicable, the flaps.
- Place the spine text centred, with a margin of at least 1 mm on each side (more if the spine is thin), because the fold may shift slightly.
Sources
- Arctic Paper, Munken Print Cream technical data sheet: https://preproduction.arcticpaper.com/globalassets/arcticpaper.com/documents/backup-tds-products/1-munken/en/munken-print-cream.pdf
- Arctic Paper, Arctic Matt technical data sheet: https://preproduction.arcticpaper.com/globalassets/arcticpaper.com/documents/backup-tds-products/5-arctic/en/arctic-matt.pdf
- Arctic Paper, Arctic Silk+ technical data sheet: https://preproduction.arcticpaper.com/globalassets/arcticpaper.com/documents/backup-tds-products/5-arctic/en/arctic-silk-plus.pdf
- Arctic Paper, Arctic Volume White: https://www.arcticpaper.com/our-products/our-brands/arctic-volume/arctic-volume-white/
- Arctic Paper, Amber Graphic technical data sheet (distributed by Paper.co.uk): https://www.paper.co.uk/wp-content/uploads/2025/01/Amber-Graphics-Data-Sheet-11-24.pdf
Frequently asked questions
How do I calculate the spine width of a book?
Number of inside pages ÷ 2 × thickness of one sheet in mm. Example: 200 pages on a 0.12 mm paper give a 12 mm spine.
Where can I find the thickness of my paper?
On the manufacturer's technical data sheet (in µm) or from the printer. Failing that, multiply the grammage by the paper's bulk.
Should I add the thickness of the cover?
Often yes, for a few tenths of a millimetre, especially with a thick or hard cover. The printer will give you the exact value: use it.
Why divide the number of pages by 2?
Because one sheet (a leaf) carries two pages, one on the front and one on the back.
Is my calculation 100% reliable?
No: the actual thickness varies by a few percent depending on the paper batch, humidity and binding. Have the printer approve the cover template.
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