Five causes account for most coloring-book interior rejections: low resolution (KDP defines under 200 DPI as low resolution, and recommends a minimum of 300 DPI), gray or blurry edges that read as low quality even at correct DPI, content placed outside the safe margin, a gutter that doesn't match the file's actual interior page count, and a file size or format issue on upload (the interior PDF cap is 650 MB). Each maps to one specific check, and passing four of five still fails the book.
The five, side by side
| # | Cause | What KDP's guidance says |
|---|---|---|
| 1 | Low resolution | Recommends a minimum of 300 DPI; defines anything under 200 DPI as low resolution |
| 2 | Gray or blurry edges | A file can carry a 300 DPI tag and still look blurry from an altered tag or an out-of-focus source |
| 3 | Content outside the safe margin | Outer margin minimums (0.25 in no-bleed, 0.375 in bleed) plus the gutter, on every edge |
| 4 | Gutter mismatched to page count | Gutter band is set by interior page count (0.375 in up to 150, 0.5 in from 151-300, wider above that) |
| 5 | File size or format | Interior upload capped at 650 MB; fonts must be embedded |
Why resolution and blur are counted separately
These are two different failures that both read as "the lines look bad." Resolution is too few pixels for the print size — a file exported smaller than the trim needs at 300 DPI. Blur is a color-depth problem — gray, anti-aliased, or JPEG-compressed pixels along an otherwise correctly sized line, which a printing press reproduces as a dot pattern instead of a solid edge. A file can fail either one independently of the other, which is why fixing resolution alone doesn't always fix a "flagged as low quality" rejection — see the DPI guide and the gray-pixel guide for each in full.
Why margin and gutter problems are easy to miss
Safe margins and the gutter are both about keeping content clear of edges that either get trimmed or disappear into the binding, but they're set by different things — margins by a fixed inch minimum, the gutter by interior page count — so a page that respects one can still violate the other. A single-sided book that doubled its interior page count by adding blank backs (see the gutter guide) can cross into a wider gutter band without anyone noticing, because the art itself didn't change; only the page count driving the gutter calculation did.
Why file-level problems slip past page-by-page checks
Checking every page individually for resolution and margins doesn't catch a mismatch between the declared page count and what the assembled file actually contains, or a gutter set for the wrong band once the final page count is locked in. These are file-level, not page-level, and they're the reason a checklist should include a completeness pass — every page present, none missing or failed — after the page count is final, not before (see the interior PDF checklist guide for the full six-check order).
What isn't on this list
Content policy violations (prohibited subject matter) and metadata mismatches (a title or description that doesn't match the actual book) are also real rejection paths, but they're not formatting problems and this page doesn't cover them — KDP's content guidelines are the relevant reference there, not an interior-file spec.
Catching these before upload
CrayonMill's export check runs six checks automatically before the download button unlocks — every page ready with none failed, 1-bit color depth, interior page count inside CrayonMill's supported 24–300 window (KDP itself allows more), the gutter matching that count, the outer safe margin, and resolution — which covers causes 1 through 4 above at the file level. It doesn't replace KDP's own review, but it catches the most common causes before a file ever reaches KDP's queue.
Sources
Last verified 2026-09-04. Updated 2026-09-04.