Getting a "file failed our review" email from KDP after you've already announced a launch date is miserable. Almost every rejection traces back to one of a handful of measurable numbers: trim size, bleed, margins, spine width, DPI. Here's the checklist, in full.

1. Page size: trim and bleed

Your PDF page size has to be exact. Anything with art running to the edge needs bleed — KDP adds 0.125" to the outside edges for that.

Trim size → PDF page size with bleed:

US comic single issue — 6.625" × 10.25" → 6.75" × 10.5"
Manga / digest — 5" × 7.5" → 5.125" × 7.75"
Trade paperback — 6" × 9" → 6.125" × 9.25"
Workbook / art book — 8.5" × 11" → 8.625" × 11.25"

bleed page width = trim width + 0.125 · bleed page height = trim height + 0.25

Keep anything that must not be cut (lettering, panel borders you care about) at least 0.375" inside the trim edge.

2. Interior margins and gutter (KDP paperback)

Page count → inside gutter / outside margin (no bleed) / outside margin (with bleed):

24–150 pages — gutter 0.375", outside ≥ 0.25" (no bleed) / ≥ 0.375" (with bleed)
151–300 pages — gutter 0.5", outside ≥ 0.25" / ≥ 0.375"
301–500 pages — gutter 0.625", outside ≥ 0.25" / ≥ 0.375"
501–700 pages — gutter 0.75", outside ≥ 0.25" / ≥ 0.375"
701–828 pages — gutter 0.875", outside ≥ 0.25" / ≥ 0.375"

3. Spine width (paperback cover math)

Black & white, white paper: pages × 0.002252"
Black & white, cream paper: pages × 0.0025"
Standard color: pages × 0.002252"
Premium color: pages × 0.002347"

full cover width = back trim + spine + front trim + 0.25" bleed · cover height = trim height + 0.25"

Spine text needs roughly 100+ pages of thickness to read at all — keep it 0.0625" away from the spine edges either way.

4. Color, resolution, files

All raster art at 300 DPI at final print size — never upscale to get there.
KDP accepts RGB PDFs and converts to CMYK; expect slight darkening of saturated colors.
Body text and lettering in pure black, not rich black or dark-gray builds.
All fonts embedded in the PDF.
Transparency flattened; no layers, comments, or form fields.
One single PDF for the interior; the cover is its own single-page PDF.
Page count is even and matches what you enter in KDP.
No trim marks, registration marks, or color bars in the file.

5. The ten classic rejection causes

Wrong PDF page size for the trim you selected
Art meant to bleed that stops at the trim line
Live text or panels drifting into the gutter
Fonts not embedded
Images below 300 DPI (soft, pixelated print)
Cover spine width wrong for the page count
Barcode zone on the back cover not kept clear (2" × 1.2")
Interior page 1 starting on the wrong side (odd pages are right-hand)
ISBN/imprint page mismatch with KDP metadata
Copyrighted content you cannot prove rights to

6. Digital siblings (webtoon & CBZ)

Webtoon strip: 800 px wide, episodes sliced into pieces no taller than 1280 px, JPG/PNG under 20 MB per episode.
CBZ: page images numbered in reading order, RGB, 2000 px+ on the long edge reads well on tablets.

Standards above are the long-stable published ones — before a big print run, always verify current values on KDP's own print specifications page.

Get the templates: the Print-Ready Pack has the trim/bleed page templates above (comic, book, webtoon) as ready-to-use files, plus this checklist as a PDF.

Disclosure: this post and the pack it links to are put together by Sloom Studio, the app used to make the templates.