Glossary · Printing & files
What is spine width and how is it calculated?
Definition
Spine width: Spine width is the thickness of a printed book's spine. It equals page count × paper thickness per page, so it depends on page count and paper type.
The spine is the strip of cover that wraps around the bound edge of a book and faces outward on a bookshelf. Its width depends on how many pages the book has and how thick the paper is: spine width = page count × thickness per page. Printers publish the per-page figure for each paper stock.
For example, Amazon KDP publishes 0.0025" per page for cream paper and 0.002252" for white paper. A 300-page book on cream paper therefore has a spine of about 0.75". The same book on white paper is slightly thinner. Other printers use their own figures — check the platform's current paper specifications.
Spine width matters because the cover is a single file that wraps from back to front. If the spine on your file is wrong, the title can creep onto the front or back cover, and the printer may reject the file. Your page count must be final before the cover is: any edit that changes the page count changes the spine.
Very thin books may not be allowed to have text on the spine at all, because a narrow spine cannot be printed and folded precisely enough. KDP, for instance, currently requires at least 80 pages for spine text. Even on wider spines, leave a little margin on each side of the text.