Enter your final formatted page count and paper stock to get the exact spine width in inches and millimetres, calculated from Amazon KDP’s published paperback specifications. Free, no signup. Add your trim size for the full cover size and a working template.
The inch figure is the publication dimension — KDP reads the physical size of the PDF you upload.
We do not have an automated cover checker yet. These are the conditions Amazon applies that you can verify yourself, in the order you will hit them — check them against the numbers above.
Came for the full wrap rather than the spine? The KDP Cover Size Calculator leads with it and adds the pre-upload checklist.
Spine width is the effective page count multiplied by the caliper of the stock you print on — nothing else enters the product, which is why this tool can answer before it knows your trim size. The caliper of each stock is shown beside it in the paper menu. Amazon’s US store lists five interior and paper options and this tool supports all five; other marketplaces publish a different set, so if you are printing outside the US store, cross-check against KDP’s own calculator.
Page counts round up to the next even number before anything else happens, because interiors print on sheets. That rounded figure is the effective KDP page count, and it is what the spine is computed from.
What the trim size DOES decide is whether Amazon will print your book at that length. The legal range is a property of the trim and the stock together — cream reaches 776 pages at 6 × 9 and stops at 550 at 8.5 × 8.5, and A4 has no standard-colour option at all — so the page range is only checked once you add a trim. All 16 trims and their per-stock ranges are transcribed from Amazon's own specification table.
The inch figure is the publication dimension: KDP reads the physical page size of the PDF you upload. The pixel figure is a 300 PPI design-canvas reference only — a vector cover at the correct inch size is correct whatever pixel dimensions it does or does not contain.
Transcribed from Amazon KDP’s published paperback cover and trim-size guidelines, US store (kdp.amazon.com). Last verified 27 August 2026.
The total number of pages in your final formatted interior PDF — the figure your layout program reports for the file you are going to upload. Not sheets of paper, not the last printed page number, and not a word-count estimate. Front matter, blank versos and the copyright page all count, because they are all printed on.
KDP rounds an odd manuscript page count up to the next even page, because interiors are printed on sheets that carry two pages each. The rounded figure is shown as the effective KDP page count and it is what the spine is calculated from. Your PDF does not have to change — Amazon adds the blank page itself — but the spine has to be sized for the book that comes off the press.
Amazon prints spine text from 80 pages up; below that a cover carrying spine text is rejected. Clearing that rule is not the same as having room, though. Take 0.0625 in of fold clearance off each side and what is left is the usable width, which the calculator shows. Our own wrap renderers need about 0.225 in of total spine before they will set any type — our floor, not Amazon's — and below it the honest design is a solid colour or a pattern.
Recalculate and re-export. Every page adds its caliper to the spine, so twenty pages added in copyediting widen the wrap by roughly 0.045 in on white stock and shift the front panel by the same amount. KDP compares the cover file against the interior you upload with it, and a mismatched spine is one of the most common size rejections. The front artwork itself does not need regenerating — only the wrap geometry moves.
The spine width alone is enough to sanity-check a wrap someone else built, to size a spine text block, or to see whether your book can carry a spine title at all. If you are making the cover file yourself you need the full cover size — the single flat page that holds back cover, spine and front cover plus bleed. Add your trim size above and this page gives you both, along with a marked template.