KDP book margins and gutter: the 2026 spec, explained
The exact margin and gutter rules a KDP paperback interior must meet — the page-count gutter table, mirrored margins, trim sizes, and why Word exports get rejected — with a checklist to verify your own PDF.
Editorial
Every rejected KDP interior fails for one of a very short list of reasons, and margins are at the top of it. The rules themselves are published and stable — what trips authors up is that two of them can't be checked until the book is fully typeset. This guide lays out the complete spec, the gutter-by-page-count table, and a checklist you can run against any interior PDF before uploading it.
The four geometry rules KDP enforces
1. The PDF page size must equal your trim size — exactly. If you chose 6×9 in, every page in the PDF must measure 6×9 in (432×648 pt). The most common failure is exporting from Word at the default US Letter size: the previewer either rejects the file or shrinks your pages to fit, which wrecks the margins you set.
2. Outside margins must be at least 0.25″ (no-bleed). Top, bottom, and outside edges all need a quarter inch minimum. In practice, professional interiors use far more — 0.5″ outside and 0.6–0.8″ top and bottom — because minimum-margin pages look like a form, not a book.
3. The inside margin (gutter) must meet the page-count table. Binding swallows part of every page, and thicker books curve more at the spine. KDP's floor:
| Page count | Minimum inside margin |
|---|---|
| 24–150 | 0.375″ |
| 151–300 | 0.5″ |
| 301–500 | 0.625″ |
| 501–700 | 0.75″ |
| 701–828 | 0.875″ |
Notice the trap: you can't finalize the gutter until you know the final page count, and the final page count depends on the margins. Professional typesetting renders the book, counts pages, then re-renders with the right bracket. Doing this by hand in Word means guessing.
4. All fonts must be embedded. A print PDF must carry its fonts inside the file. Word's PDF export embeds inconsistently depending on version and settings, and "font not embedded" is a silent, common rejection.
Mirrored margins: the part Word makes hard
A book's margins are not symmetric — the gutter sits on the inside edge, which is the right side of left-hand pages and the left side of right-hand pages. Word's "mirror margins" setting exists but interacts badly with section breaks, headers, and different-first-page settings the moment your book has real front matter and chapters. This is the point where most DIY formatting attempts either stall or ship subtly wrong.
A checklist for any interior PDF
Before uploading to KDP, verify:
- Every page measures exactly your trim size (open the PDF's properties, not just one page).
- Page count is between 24 and 828.
- Inside margin meets the table above for your actual page count.
- Fonts are embedded (in Acrobat: File → Properties → Fonts — every font should say "Embedded Subset").
- Chapters open on right-hand pages, with no running head on opener pages.
If you'd rather have all five checked mechanically, Ceeryo's KDP formatter runs exactly this preflight on every interior it produces — the gutter bracket is computed from your book's real page count, and the report shows each check passing before you download.
Related reading
Update — August 2026: measured page counts per trim
We typeset the same 90,000-word manuscript at every trim Ceeryo supports and counted the pages that came out — because the gutter bracket that applies to your book depends on the typeset count, not the manuscript's:
| Trim | Pages (90k words) | Gutter bracket triggered |
|---|---|---|
| 6 × 9 in | 217 | 0.5″ (≤300pp) |
| A5 | 245 | 0.5″ (≤300pp) |
| 5.5 × 8.5 in | 253 | 0.5″ (≤300pp) |
| 5.25 × 8 in | 291 | 0.5″ (≤300pp) |
| 5 × 8 in | 314 | 0.625″ (301–500pp) |
Note the last row: the identical book crosses into the next gutter bracket purely by trim choice. If you're near a bracket boundary, check the measured words-to-pages data or run your own manuscript through the margin checker.