Why your cover is a different size at KDP and IngramSpark (and how to get it right first time)
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R. S. Breed Founder
A paperback cover is one wide image: back, spine and front, plus a strip of bleed all round that's trimmed off. The spine's width comes from your page count and how thick that printer's paper is, so the same book needs a slightly different cover at KDP, IngramSpark and Lulu.
For example, KDP works out its spine as page count times paper thickness: 0.0025 in a page for black-and-white on cream, 0.002252 in on white. A 300-page cream paperback has a 0.75 in spine at KDP. Other printers use their own paper and their own numbers.
The free calculator here does it for KDP, IngramSpark, Barnes & Noble Press, Lulu, Bookvault and Draft2Digital Print at once: https://bervet.com/tools/spine-width-calculator
For each platform you get:
- whether it prints your trim size, paper and page count at all
- the spine width and the full cover size, in inches and millimetres
- a cover template to give your designer (PDF, PNG or SVG)
- the interior setup: page size and minimum margins for your page count
If you add your cover and interior PDFs, it checks them too: size, bleed, fonts, image resolution, text too close to the edge and the barcode area. It draws each platform's guides over your cover so you can see where things will be trimmed. Every problem it finds says what to tell your designer.
The calculator is open to everyone; checking your own files is free for members and runs in your browser. Nothing is uploaded.
Each platform also has its own page, for example https://bervet.com/tools/spine-width-calculator/kdp