# Calculating the spine width of a book or booklet

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

1. Choose the inside paper with the printer and ask for **its thickness or bulk**.
2. Calculate the spine with the formula (or the [calculator](https://imprimeur.paris/en/guides/calculateurs/)).
3. Ask the printer for the **cover template**: it shows the exact spine width, the bleed and, where applicable, the flaps.
4. 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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Updated on 1 November 2026. Source : https://imprimeur.paris/en/guides/epaisseur-dos/