KDP spine width calculator
Enter your page count, trim size and paper. You get the spine width and the exact size your full cover PDF has to be — using Amazon's own formula, with nothing added to it.
The formulas
Spine width = page count × paper thickness. Cover width = 0.125" bleed + back cover + spine + front cover + 0.125" bleed. Cover height = 0.125" + trim height + 0.125".
| Paper | Thickness per page |
|---|---|
| Black & white on white | 0.002252" |
| Black & white on cream | 0.0025" |
| Premium colour | 0.002347" |
| Standard colour | 0.002252" |
Inside margins change with thickness
The gutter — the inside margin, against the spine — has to grow as a book gets thicker, or the text disappears into the binding. KDP's table: 0.375" up to 150 pages, 0.5" to 300, 0.625" to 500, 0.75" to 700, and 0.875" beyond that. Outside, top and bottom need at least 0.25", or 0.375" if you use bleed.
What will it earn?
Spine width settles whether the cover prints. What it earns is a different sum: printing cost depends on page count, ink and trim size, and comes off your royalty. There is a royalty calculator here too — worth a look before you settle on a page count, because every page costs about a penny to print.
Two rules people miss
Spine text needs 79 pages. Below that KDP wants the spine left blank — the spine is too narrow to print on reliably.
Leave the barcode area clear. Keep a 2" × 1.2" clear space in the lower right of the back cover. Amazon prints a barcode there, and artwork underneath it will be covered.
Making a puzzle book?
Puzzle Press generates the whole paperback — word search, sudoku or maze puzzles with solutions, laid out to these specifications — and then the matching cover, with the spine already worked out from the page count of the book it just made. Free to use — pay only to remove the watermark.
Make a book freeSee a finished book (PDF) · and its cover — made with it, nothing mocked up.