How spine width is calculated

The formula

Spine width = page count × thickness of one page.

That is all. Trim size does not affect it, and neither does the binding: a hardcover's board adds to the overall cover size through its wrap, not through the spine figure used in this calculation.

Paper thickness

The per-page thickness depends on the paper stock:

• White: 0.002252" per page
• Cream: 0.0025" per page
• Colour: 0.002347" per page

Worked examples

A 200-page book on white paper: 200 × 0.002252" = 0.450".

The same book on cream paper: 200 × 0.0025" = 0.500".

On colour paper: 200 × 0.002347" = 0.469".

A 800-page book on cream paper — the widest spine this app will calculate — is 2.000".

Using the number

Calculate spine width from the final page count of the exact PDF you will upload, including blank pages and front and back matter. Then build the cover around it. If the page count changes by even a few pages, recalculate: the spine sits at the centre of the cover, so a change moves the front panel.

Below 79 pages, leave the spine free of text; KDP will not print it.

Why page count must be exact

Each page adds a small fraction of an inch, so a few pages make a visible difference. Twenty extra pages on cream paper add 0.050" to the spine — enough to push spine text towards a fold and move the front panel's artwork off-centre.

Page counts also change for reasons that are easy to miss: a new blank page before a chapter that must start on the right, a revised index, or a different export setting that reflows the text. Treat the spine width as derived from the final interior file, and recalculate it every time that file changes.

Hardcover spines

A hardcover's spine also has to account for the boards and the hinge, so KDP's hardcover template can differ from a straight page-count calculation. Use this formula to understand and plan the cover, and check the final hardcover template against KDP's own cover calculator before printing.