Use the final interior page count
The spine must fit the actual printed book. Count the complete interior PDF, including front matter and blank pages, rather than the numbered pages alone. A last numbered page of 240 does not necessarily mean a 240-page file.
A planning estimate is useful while writing. It is not the number to use for final cover preparation. Freeze the interior first, then confirm the count used by the printer.
Paper changes the calculation
For a KDP black-ink paperback on cream paper, multiply the page count by 0.0025 inches. A 240-page interior therefore has a calculated spine of 0.6 inch. The calculator includes KDP’s other listed paper factors too. These figures are not IngramSpark measurements.
A 6 × 9 inch cover for that example has two 6-inch panels, the 0.6-inch spine and 0.125-inch bleed at each outside edge: 12.85 × 9.25 inches overall. Use the official template to place text and the barcode.
Do not force text onto a narrow spine
KDP’s current guidance requires at least 79 pages for spine text, or 80 when using Cover Creator. A short book may need a plain spine. The printer’s template and current rules take precedence over a rough mockup.
Avoid placing a narrow colored border exactly along the spine edges. Small manufacturing shifts become more visible when the design depends on perfect alignment. Review the full wrap, not only the front cover.
Finish with the printer’s template
Use our calculator to understand the dimensions and discuss the design. Generate the final template with the selected printer after the interior is complete. Hardcover construction needs a different template from paperback.
If the page count changes, check the cover again. Keep the interior and cover version names paired so an old cover is not accidentally uploaded with a revised manuscript. Our cover-preparation service works from supplied artwork and the agreed printer specification.
Official references
Check the current requirements for your chosen edition before final export.