Home › Fixing a KDP gutter rejection
This is a diagnostic, not an explainer. Work down it in order — the causes are listed by how often they turn out to be the real one, and the first two are both cases where nothing looks wrong in your file.
Amazon checks margins at two separate stages, and they fail differently. Knowing which one you hit narrows the cause immediately.
The second case is the confusing one, and it is common enough to be worth stating plainly: a file can clear Print Previewer and still be rejected by the manual review for margins. If that happened to you, the automated check is not lying — the two checks are not identical, and passing the first does not guarantee the second.
Amazon calls the inside margin the gutter, and its minimum grows with page count. From KDP’s own margin table:
| Page count | Inside (gutter), minimum |
|---|---|
| 24–150 | 0.375″ (9.6 mm) |
| 151–300 | 0.5″ (12.7 mm) |
| 301–500 | 0.625″ (15.9 mm) |
| 501–700 | 0.75″ (19.1 mm) |
| 701–828 | 0.875″ (22.3 mm) |
Outside, top and bottom margins do not scale — they are at least 0.25″ without bleed and at least 0.375″ with bleed, at every page count.
Two things about that table that cause most of the trouble. First, some software has separate “inside margin” and “gutter” fields; Amazon’s guidance is to put the same value in both. Second, Amazon itself advises setting margins slightly larger than these minimums. The published numbers are a floor, not a target — formatting at exactly the minimum is how books fail on a rounding error.
Most likely if: this book passed before, or it is volume two of something that passed, and you added content.
The tiers above are steps, not a slope. A 148-page book needs 0.375″. Add two puzzles and at 152 pages it needs 0.5″ — the margins that were correct last week are now insufficient, and nothing about your layout changed.
There is a second-order version of this that catches people out: Amazon recalculates the page count from your uploaded file and rounds it up to an even number. A 149-page manuscript becomes 150. If a reflow pushes you from 150 to 151, you have moved a tier without adding a visible page.
How to tell: check your final page count in Print Previewer, not in your authoring tool, and read it against the table above.
Fix: raise the inside margin to the tier your actual page count sits in, and add a little on top.
Most likely if: the error points at a page where the margin area is visibly empty.
This is Amazon’s own documented explanation, and it surprises nearly everyone. The checker measures characters and spaces, not ink. Two causes it names specifically:
How to tell: turn on formatting marks in your authoring tool and look at the flagged page’s line endings. If your book was assembled by hand in a word processor, this is a strong candidate.
Fix: delete the trailing whitespace, and widen the margins beyond the minimum so italic overhang has somewhere to go.
A related symptom worth knowing: Print Previewer does not only reject: it will also try to fix some problems by scaling or reflowing content to fit. If your pages come back looking subtly different sizes from one another, invisible characters are usually why.
Most likely if: your pages carry a background colour or a full-page graphic.
Amazon’s own first suggestion for a margin error on pages with a background is to switch the bleed setting to “Bleed”. Bleed also changes the page size arithmetic: add 0.125″ to the width and 0.25″ to the height, so a 6×9 book becomes a 6.125×9.25 page. If your PDF was built at trim size but uploaded as a bleed book, or the reverse, everything sits in the wrong place relative to the margins.
How to tell: compare the page dimensions of your PDF against the arithmetic above.
Fix: make the file and the setting agree. Also note that with bleed, the outside minimum rises to 0.375″.
Most likely if: you re-uploaded an interior and reused a cover that worked before.
A KDP wrap cover is one flat image: back, spine, front. The spine width is a function of page count and paper stock. Change the interior and the correct spine width changes with it — so a cover built for the previous version is now the wrong size, and the rejection appears to be about the cover.
How to tell: did the interior page count change since the cover was made? If yes, this is almost certainly it.
Fix: regenerate the cover at the current page count. Our spine width calculator does this for free, and gives you a 300 DPI blank template with the trim, bleed and barcode zones marked.
Most likely if: you set 0.375″ because the table said 0.375″, and nothing above applies.
Amazon’s documentation advises exceeding the minimums, and formatting tools tend to agree — one well-known book formatter ships a default inside margin of 0.875″, far above the floor for a short book, precisely to keep this from happening.
Fix: add an eighth of an inch to the inside margin and resubmit. It costs a little page area and removes a whole class of failure.
You will see phrases like “insufficient gutter” and “this text is outside the margins” quoted around the web, including in publisher forums where people report exactly what they saw. Worth knowing: Amazon’s own help pages never reprint these strings. The official documentation frames the problem as questions — is content outside the margins, does it extend into the gutter — rather than as literal messages.
So if the wording you got does not match what a forum post says, that is not a sign you have a different problem. The underlying check is the same one, and the causes above are the same causes.
Every cause above except the invisible characters comes down to one thing: a number that depends on page count, fixed at a moment when the page count was different. The gutter, the spine width, and the bleed arithmetic are all derived values, and hand-maintaining derived values is what breaks.
PuzzleBindery recomputes the gutter from the live page count on every export, and the wrap cover reads the same live page count for its spine width. Add a puzzle, and both move on their own. There is no field to forget.
It is free to check: build the book, export the watermarked preview, and take it through Print Previewer before paying for anything.
Rebuild the interior with margins that follow the page count.
Open the Studio →Margin figures on this page are taken from Amazon KDP’s own published margin table and formatting help, read on 10 September 2026. Amazon changes its requirements from time to time — check the current figures before you submit. Reported error wording is drawn from publisher forum posts and is attributed as such above.
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