Paperback cover & spine calculator
Pick a trim size, page count and paper. You get every number a print cover and interior need, in inches, millimetres and 300 DPI pixels, plus a check of the files you already made.
How it works
Most rejected paperback uploads fail on a few numbers: a cover made before the final page count so the spine is too narrow, bleed added twice, an interior without the extra 0.125 in, a gutter margin too small for a thick book, or spine text on a book under 80 pages.
How to use it: choose the trim size (or type a custom one in mm or inches), enter the page count of the final interior PDF, choose the paper and tick bleed if pictures or colour reach the page edge. Press Calculate. To check finished files, type their page sizes in the optional boxes.
Numbers follow KDP’s published paperback rules (paper thickness per page, 0.125 in bleed, gutter by page count). For IngramSpark, hardcover or a local printer, choose “Other printer” and type their paper thickness, and use their template if they offer one. Always check the final upload in KDP’s previewer.
FAQ
Is anything uploaded?
No. It is only arithmetic in your browser.
Why does the spine change when I add pages?
Spine width is page count × paper thickness. Make the cover last, after the page count is final.
Does it read my PDF?
No. Type the page sizes your design program or PDF viewer shows, and it compares them.