KDP spine width, and when you can put text on it

The spine is as thick as the pages inside it, so it depends on two things: the page count and the paper.

The formula

Spine width = page count × paper thickness per page.

Paper	Inches per page	200 pages	400 pages
Black ink, white paper	0.002252	0.450 in	0.901 in
Black ink, cream paper	0.0025	0.500 in	1.000 in
Standard color, white paper	0.002252	0.450 in	0.901 in
Premium color, white paper	0.002347	0.469 in	0.939 in

Text on the spine

KDP allows spine text on paperbacks of more than 79 pages, so at least 80 pages. On a thinner book the spine is too narrow and any text would wrap onto the front or back.

Keep spine text 0.0625 in away from each fold: the fold can move by about 0.0625 in in printing.

When the page count changes

Add or remove pages and the spine changes, so the cover has to be made again at the new width. In kdpbookai the cover is rebuilt from the page count each time you make the files.

Sources

KDP help pages, checked November 7, 2026. KDP changes its rules without notice; the linked page has the final word.