Spine width calculator
Spine width, full cover size and whether your book is thick enough for spine text — for Amazon KDP and IngramSpark. Every multiplier and formula this uses is published further down the page, with the printer's own source and the date we last read it.
Print rules last verified —. Everything runs in your browser; nothing about your book is sent anywhere.
The formula
Spine width is the page count multiplied by a per-page paper thickness. That is the whole calculation, and it is the same one Pagequire uses internally:
spine width = page count × thickness per page
A full paperback cover is then the back cover, the spine and the front cover laid flat, plus 0.125 in of bleed on every side:
cover width = 0.125 + trim width + spine + trim width + 0.125
cover height = 0.125 + trim height + 0.125
A hardcover case adds a wrap on all four sides, and on KDP a hinge on each side of the spine. IngramSpark uses a wider wrap and no hinge.
The multipliers, and where they come from
These are the numbers most calculators do not show you. Thickness per page, in inches:
| Paper and ink | Inches per page |
|---|
| Group | Source | Last read |
|---|---|---|
| Spine multipliers | — | — |
| Cover geometry | — | — |
Spine text
Neither printer will let you put type on a spine that is too thin to hold it. KDP requires at least 79 pages; IngramSpark allows it from 48. Above that threshold, keep the type inside the spine width less 0.0625 in of clearance on each side — binding drifts, and a title that touches the fold is a title that gets trimmed into the front cover.
What this does not tell you
It is arithmetic against published specifications, not an approval. Paper stock varies between print runs, and a spine measured to three decimal places can still come back a hair out. Build your cover to these numbers, then check the printer's own previewer before you approve a proof. Acceptance is always the printer's.
If a number here ever disagrees with the printer's current page, the printer is right and we want to know: [email protected].