Gutter (inside margin) Defined.
Definition
The gutter is the inside margin of a printed book: the space between the text and the fold where pages meet the spine. KDP sets a minimum gutter that grows with the page count, because a thicker book curves more at the binding, and text set too close to the fold disappears into it.
Sources checked 20 October 2026.
How it works
KDP's margin table sets the minimum inside margin in steps by page count, from its shortest books to its longest, while the top, bottom and outside margins have a single minimum that is larger for books with bleed. Because left and right pages are bound on opposite sides, the gutter sits on the right of a left-hand page and on the left of a right-hand page. Some software has separate fields for the inside margin and the gutter; KDP's advice is to enter the same value in both.
An example
A short workbook and a long handbook with the same trim fall into different rows of KDP's table, and the handbook's minimum gutter is larger. If the workbook later grows past the row's upper limit because you add chapters, its interior has to be reset with the wider gutter before you upload it again: KDP warns that a file without proper sizing may be rejected on upload or print badly.
Common mistakes
Using one margin all round, copied from a document template, so the outside margins are generous and the inside one is too narrow. Adding pages without checking whether the book has crossed into a new row of the margin table. And running a two-page image across a spread without allowing for the fold, where the middle of the picture is lost.
