How do I work out the spine width for my book?
Updated 22 September 2026
Multiply the page count by the paper thickness per page: about 0.0025 inch for cream and 0.0022520000000000005 inch for white on KDP. A 120-page white-paper book has a spine about 0.27 inch wide, which sets how wide the full cover has to be.
The spine width is a straight function of the page count and the paper: page count times the per-page thickness. KDP uses about 0.0025 inch a page for cream and 0.0022520000000000005 inch for white, so a 200-page white book runs near 0.45 inch. The spine has to be right or the cover art and title sit off-centre. The free KDP cover calculator works it out from your trim, paper and page count.
Publisher Studio works the spine out from the final page count, after it evens the total, and gates the cover on it, so you do not do the arithmetic by hand. Very thin books get no printed spine text, which the studio flags rather than letting the title crawl onto the front.