A cover that looks finished can still fail at the KDP upload step. When it does, the error is usually not about the artwork. It is a number that came from a different version of the book.
I maintain the sizing calculator at BookCoverGen, and the same handful of mismatches show up in support mail. Here they are in the order they cost people the most time.
The only arithmetic that matters
A print cover is one flat file:
- width = panel + panel + spine + 0.25 in
- height = trim height + 0.25 in
The 0.25 in is 0.125 in of bleed on each outside edge. The panels come from the trim size. The spine comes from page count times paper thickness.
For 6 x 9 in at 300 pages on black-and-white white paper, KDP's per-page figure is 0.002252 in, so the spine is 0.676 in and the full wrap is 12.93 x 9.25 in. Every case below is that calculation going wrong in a different place.
1. Your page count changed after the cover was built
This one gets caught in the previewer, not at your desk.
Re-paginate a manuscript and the spine moves. 6 x 9 at 250 pages on white paper is 0.563 in. At 300 pages it is 0.676 in. That is 0.113 in, close enough to an eighth of an inch, and it lands exactly where the author name sits on the spine. On a fold, an eighth of an inch is the difference between centered and cut.
Build the cover after the final proof, not after the first draft. If the interior changes, re-run the calculation before the next upload.
2. The paper changed, the cover did not
KDP's spine math is per paper type:
- black-and-white white paper: 0.002252 in per page
- black-and-white cream paper: 0.002500 in per page
- premium color white paper: 0.002347 in per page
At 300 pages the white-paper spine is 0.676 in. The same 300 pages on cream is 0.750 in. The file has to grow by 0.074 in, and the front and back panels shift outward with it. Switch paper at the pricing step and keep the old cover, and the spine type is off the fold.
3. The file has no bleed, or bleed on two edges
A print file is trimmed after it is printed. The artwork has to run past the trim line on the top, bottom and outside edges, which adds 0.25 in to both dimensions.
Two common versions of this:
- the file is built at trim size (12 x 9 in for 6 x 9 at 300 pages, not 12.93 x 9.25 in);
- the designer adds bleed at the outer edges of the front and back panels but not across the spine wrap.
Both look fine on screen, because the missing strip is white and the background is white. The previewer is the first place the trim sliver shows up, and a background that stops at trim size will show a hairline at the cut.
4. The ebook cover was exported from the print panel
Ebooks have no spine, no bleed and no back cover. KDP asks for a front cover of 1,600 x 2,560 px at a 1.6 aspect ratio, JPEG or TIFF, under 50 MB.
The print panel for 6 x 9 in at 300 DPI is 1,800 x 2,700 px. The ratio is 1.5, not 1.6, so it does not simply scale down. What happens next depends on the store: the image gets cropped, padded, or rendered smaller in the thumbnail grid than a properly sized file. Export the ebook cover at the pixel size, separately from the print export.
5. Spine text on a book that will not print it
KDP prints spine text only above 79 pages. Below that the spine stays blank, so artwork should run through it and type should not be there at all. Type placed on a 40-page file does not appear in print; if the page count later grows past 79, the old file still has type set for a spine width it no longer has.
When there is spine text, it needs 0.0625 in clear on each side of the fold. Thin books have thin margins. Check the template before the title goes on the spine.
6. More than one page, fonts not embedded, images below 300 DPI
These are the boring checks that produce failed preflight:
- the wrap is one page: back cover, spine, front cover, never three separate files;
- fonts embedded, not linked;
- images at 300 DPI at final size;
- one flattened layer, no live transparency.
The barcode area on the back cover has to stay clear. The template marks where it goes.
Before you upload, check these six
- Final page count, after the last proof.
- The paper type you will actually print on.
- Full wrap = panels + spine + 0.25 in.
- Bleed 0.125 in on the top, bottom and outside edges.
- Spine text only over 79 pages, 0.0625 in clear on each side.
- Ebook cover exported at 1,600 x 2,560 px, separate from the print wrap.
KDP publishes the current figures and changes them. The calculator on our site runs the same arithmetic with your page count and exports a layout guide at 1 unit = 1 inch, but the printer's template is the final word. When a file fails at upload, the error text is usually accurate about which of these six it is.
