KDP recommends 300 DPI for interior images at the printed size and defines anything under 200 DPI as low resolution. For an 8.5 × 11 in coloring page, 300 DPI is 2550 × 3300 pixels. Files at 240 DPI (the "2K" setting some generators offer) fall short of the recommendation, and upscaling a low-resolution file does not recover detail. The fix is to generate at the target pixel size, not stretch a smaller file.
The numbers that matter
DPI is not a property stored in the file — it is pixel width divided by the printed width in inches. A file can carry a "300 DPI" tag in its metadata and still be flagged as low resolution if its actual pixel dimensions are too small for the trim size it is placed into.
| Trim size | 300 DPI pixel size | Common generator output | Actual DPI |
|---|---|---|---|
| 8.5 × 11 in | 2550 × 3300 | 1024 × 1325 ("1K") | 120 |
| 8.5 × 11 in | 2550 × 3300 | 2048 × 2650 ("2K") | 240 |
| 8 × 10 in | 2400 × 3000 | 2048 × 2560 | 256 |
The "1K" and "2K" labels describe the short-side pixel count of a square generation, not a print-ready size. Neither reaches the recommended 300 DPI at full-page trim sizes, and 1K falls under the 200 DPI line KDP calls low resolution — which is why 1K files straight out of an image generator get flagged on upload, while 2K files print visibly softer than the recommendation without tripping that flag.
How to check a page
- Open the file's properties (or an image editor's document-size panel) and read its pixel width and height.
- Divide the pixel width by the trim width in inches — 8.5 for a standard US letter interior, 8 for an 8 × 10 in trim, and so on for the trim size the book actually uses.
- Anything under 300 falls short of KDP's recommendation, and anything under 200 gets flagged as low resolution; anything gray in the lines will print muddy even above 300 DPI (see the gray-pixel guide).
- Repeat the check on a spread near the middle of the file, not just the cover — interior pages are generated or exported independently and DPI can vary page to page.
Interior pages: 80 · within the supported range (24–300)
Why "upscaling" does not fix it
Resizing a 1024 × 1325 px file up to 2550 × 3300 px changes the pixel count but not the information in it — the software interpolates new pixels from neighbors that were already there. Edges that were crisp at the original size come out soft or stair-stepped at the larger size, and line art in particular loses the clean vector-like edges a coloring page needs. KDP's check looks at the file's actual pixel dimensions relative to trim size, so an upscaled file can pass the DPI gate on paper while still looking visibly worse in print than a file generated at native resolution. The only reliable fix is producing the artwork at (or above) the target pixel size in the first place.
What KDP actually checks
KDP's interior image guidance recommends a minimum of 300 DPI for images placed in a print book and defines anything below 200 DPI as low resolution, calculated from the image's pixel dimensions and the size it is displayed at in the interior file. This is a per-image check run during the review that follows upload, not a setting picked once for the whole manuscript — a single low-resolution page can hold up the rest of an otherwise compliant book. Reviewers also flag interior images with transparency or color modes that do not match the chosen print type (black-and-white interior vs. color), so DPI is one of several checks a coloring-book interior needs to clear, not the only one.
Why line art should also be 1-bit
Coloring pages are black lines on white paper. A 1-bit file has exactly two values, so the press prints solid black and clean white with no dithering. A grayscale file at the same pixel dimensions can pass the DPI check and still print muddy, because anti-aliased or gray edge pixels reproduce as soft gray rather than a clean line. CrayonMill's cleaning pipeline enforces 1-bit output before export, and the export check refuses a book that is not 300 DPI 1-bit.
Common mistakes
- Generating at a fixed square size and cropping to trim. A 2048 × 2048 px generation cropped to an 8.5 × 11 in page loses pixels on the long edge, dropping the effective DPI below the square-image number.
- Trusting an embedded DPI tag instead of pixel dimensions. Some export tools write "300" into the file's metadata regardless of actual pixel size; KDP's check is based on pixels and trim size, not the tag.
- Upscaling once, then upscaling again for a different trim size. Each resize compounds the softening described above.
- Checking only the cover file. Interior pages are exported separately and a batch job can silently drop resolution on a subset of pages.
Sources
Last verified 2026-09-04. Updated 2026-09-04.