KDP Gutter Size and Margin Requirements
Quick answer
KDP gutter size is the extra inside margin added near the binding so text does not disappear into the spine. Your inside margin must increase as page count increases, and it must be set separately from the outside margin. For a common 6x9 paperback, do not use equal left and right margins unless the book is very short and the inside margin still clears KDP's minimum. Use mirror margins in Word, confirm the final page count, then check the exported PDF before upload.
When this matters
This matters when a paperback interior has live text, page numbers, headers, tables, or graphics near the binding edge. The higher the page count, the more binding margin the book needs. A layout that looks acceptable as a flat PDF can still be hard to read after printing because the inside edge curves into the spine.
Common scenarios include 6x9 books, journals with wide tables, Word manuscripts with mirror margins disabled, and interiors that were resized after export.
Common causes
- Inside margin and outside margin are set to the same value.
- Word mirror margins are off, so odd and even pages do not alternate correctly.
- The page count changed after margins were chosen.
- Page numbers or running headers sit inside the binding risk area.
- A 6x9 book uses a generic template without checking KDP gutter size.
- The PDF was scaled during export, changing the real margin clearance.
How to check
Open the final exported PDF, not only the Word or layout file. Check odd and even pages separately. Measure the live text area from the inside page edge, confirm the outside margin separately, and inspect pages with page numbers, tables, chapter openers, and wide images. If the book is 6x9, confirm that the document size is actually 6x9 and that the selected KDP trim size matches the PDF.
In Word, use mirrored margins, set a separate gutter or larger inside margin, then export again without "fit to page" or printer scaling.
Tool
Use the Gutter Calculator to estimate inside margin and gutter size from page count before uploading.
Related KDP errors
Before uploading again
Use the pre-upload checklist and run the risk scan after you export the corrected interior PDF.