# Print calculators: book spine, page count, resolution

Three calculations to do before preparing a file or requesting a quote. The calculation runs in your browser: no data is sent and nothing is stored. Without JavaScript, use the formulas, examples and tables given for each calculator.

## Spine width

Calculate the spine width of your perfect-bound book or booklet, to prepare the cover. Formula: **spine (mm) = inside pages ÷ 2 × thickness of one sheet (mm)**. If you only know the grammage: thickness (µm) = grammage (g/m²) × bulk of the paper.

Example: 200 inside pages on a 120 µm (0.12 mm) paper give 200 ÷ 2 × 0.12 = **12.0 mm**. The bulk and thickness values offered are indicative; see the guide [Spine width](https://imprimeur.paris/en/guides/epaisseur-dos/).

| Pages | 99 µm (offset 80 g) | 110 µm (offset 90 g) | 113 µm (matt coated 115 g) | 120 µm (bulky 80 g) | 135 µm (bulky 90 g) |
|---|---|---|---|---|---|
| 48 | 2.4 mm | 2.6 mm | 2.7 mm | 2.9 mm | 3.2 mm |
| 96 | 4.8 mm | 5.3 mm | 5.4 mm | 5.8 mm | 6.5 mm |
| 128 | 6.3 mm | 7.0 mm | 7.2 mm | 7.7 mm | 8.6 mm |
| 200 | 9.9 mm | 11.0 mm | 11.3 mm | 12.0 mm | 13.5 mm |
| 300 | 14.9 mm | 16.5 mm | 17.0 mm | 18.0 mm | 20.3 mm |
| 400 | 19.8 mm | 22.0 mm | 22.6 mm | 24.0 mm | 27.0 mm |

Interactive calculator: https://imprimeur.paris/en/guides/calculateurs/#calc-dos

## Page count and number of sheets

Check whether your number of pages suits the chosen binding, how many pages to add and how many sheets will be printed. With saddle stitching (stapled booklet), **the number of pages must be a multiple of 4** and **sheets = pages ÷ 4**.

Example: a 22-page document with saddle stitching goes up to **24 pages** (2 pages to add), i.e. **6 folded sheets**. With perfect binding, the minimum is an even number of pages; with spiral binding, the number of pages is free. See the guide [Booklet page count](https://imprimeur.paris/en/guides/pagination-brochure/).

| Pages in the document | Page count to plan | Pages to add | Sheets |
|---|---|---|---|
| 5 to 8 | 8 | 8 − pages | 2 |
| 9 to 12 | 12 | 12 − pages | 3 |
| 13 to 16 | 16 | 16 − pages | 4 |
| 17 to 20 | 20 | 20 − pages | 5 |
| 21 to 24 | 24 | 24 − pages | 6 |
| 25 to 28 | 28 | 28 − pages | 7 |
| 29 to 32 | 32 | 32 − pages | 8 |
| 33 to 48 | 36, 40, 44 or 48 | — | 9 to 12 |

Table drawn up for saddle stitching, cover included (same paper as the inside).

Interactive calculator: https://imprimeur.paris/en/guides/calculateurs/#calc-pagination

## Pixels, dpi and print size

Check whether your image has enough resolution for the size you want, or how many pixels you need. Formulas (1 inch = 25.4 mm):

- **size (mm) = pixels ÷ dpi × 25.4**
- **dpi = pixels ÷ (size in mm ÷ 25.4)**
- **pixels = size (mm) ÷ 25.4 × dpi**

Benchmarks: 300 dpi for a print read up close; 100 to 150 dpi for a large format seen from a distance.

Example: a 3000 × 2000 pixel photo printed at 300 dpi measures 3000 ÷ 300 × 25.4 = **254.0 mm** by 2000 ÷ 300 × 25.4 = **169.3 mm**. See the guide [Preparing your file](https://imprimeur.paris/en/guides/preparer-son-fichier/).

Pixels needed, without bleed:

| Format | 300 dpi | 150 dpi |
|---|---|---|
| Business card 85 × 55 mm | 1004 × 650 | 502 × 325 |
| A6 105 × 148 mm | 1240 × 1748 | 620 × 874 |
| A5 148 × 210 mm | 1748 × 2480 | 874 × 1240 |
| A4 210 × 297 mm | 2480 × 3508 | 1240 × 1754 |
| A3 297 × 420 mm | 3508 × 4961 | 1754 × 2480 |
| Poster 400 × 600 mm | 4724 × 7087 | 2362 × 3543 |
| Poster 600 × 800 mm | 7087 × 9449 | 3543 × 4724 |

Interactive calculator: https://imprimeur.paris/en/guides/calculateurs/#calc-resolution

## Sources

- International inch (1 in = 2.54 cm exactly): NIST, *Special Publication 811, Guide for the Use of the International System of Units*, Appendix B: https://www.nist.gov/pml/special-publication-811
- imprimeur.paris file checkpoints (300 dpi for small formats, 100 to 150 dpi for large format; multiple of 4 for saddle stitching).
- Arctic Paper technical data sheets cited in the guides [Paper grammage](https://imprimeur.paris/en/guides/grammages/) and [Spine width](https://imprimeur.paris/en/guides/epaisseur-dos/) for the indicative bulk values.
- ISO 216 (A sizes): https://www.iso.org/standard/36631.html

## Frequently asked questions

### How do I calculate the spine width of a book?

Inside pages ÷ 2 × paper thickness in mm. The calculator does it for you, from the thickness or from the grammage and the paper type.

### How many pixels do I need to print an A4 at 300 dpi?

2480 × 3508 pixels (210 × 297 mm ÷ 25.4 × 300), without bleed.

### My booklet has 22 pages. How many sheets is that?

With saddle stitching, you have to go up to 24 pages, i.e. 6 folded sheets. The calculator also tells you how many pages to add.

### Do these calculations replace the printer's advice?

No: they give a reliable estimate for preparing your file, but the printer confirms the spine width, page count and resolution according to their equipment.

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Updated on 1 November 2026. Source : https://imprimeur.paris/en/guides/calculateurs/