Free tool

KDP margin calculator

TL;DR

KDP's required inside (gutter) margin grows with page count — 0.375in up to 150 pages, 0.5in at 151–300, 0.625in at 301–500 and up from there. That's why a template that passed Print Previewer last week fails after you add chapters: your book crossed a threshold and the template's margins are now wrong. Run your numbers below, then check the mismatch list — the fix is usually one of five things.

Trim size Ink & paper Page count Interior has bleed (images run off the page edge)

0.5in inside (gutter) margin — the one KDP enforces by page count

0.25in minimum outside, top, and bottom margins

6 × 9in exact page size your exported PDF must be — same as trim, NOT Letter

In Word: Layout → Margins → Custom Margins → set Multiple pages: Mirror margins, Inside 0.5in, Outside 0.25in (0.5in is more comfortable), Top and bottom at least 0.25in — and set Paper size to 6 × 9in, because Word exports US Letter by default and that alone fails the previewer.

Print Previewer doesn't match your file? It's one of these five

You uploaded the Word file instead of a PDF. KDP re-converts .docx on their servers — fonts get substituted and text reflows, so the preview differs from your screen even when your file is right. Export to PDF and upload that.
The PDF's page size isn't your trim size. Word exports 8.5 × 11 Letter unless you set the paper size to the trim. KDP then scales or crops the page and everything shifts.
Your page count crossed a gutter threshold. Templates are built for a page-count range. Add enough pages to cross 150, 300, 500, or 700 and the required inside margin grows — the calculator above gives the current number.
Fonts aren't embedded. If the PDF references fonts instead of embedding them, KDP substitutes its own and line breaks move. In Word's PDF export options, tick "ISO 19005-1 (PDF/A)" to force embedding.
Bleed mismatch. If any image runs to the page edge, the whole PDF must be trim + 0.125in per outside edge and you must select "Bleed (PDF only)" on KDP's print options — bleed content in a no-bleed setup (or vice versa) shifts every page.

Sizing the cover next? The spine width calculator gives the exact wrap dimensions for your final page count.

Or never think about margins again. ebookdone outputs the print-interior PDF with the gutter computed from your actual page count — mirrored margins, embedded fonts, correct page size, passes Print Previewer as generated — plus the wrap cover, EPUB, and KDP metadata, from $9 per book.

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