KDP's inside margin (gutter) is set by interior page count, not trim size: 0.375 in for 24–150 pages, 0.5 in for 151–300 pages, and it keeps stepping up for thicker books. A single-sided coloring book with 76 art pages has a 152-page interior — already past 150 — so it needs the 0.5 in gutter, not the 0.375 in one a page-count glance might suggest.
The full gutter table
KDP publishes one gutter band table for every paperback, coloring books included. The bands are set by the number of pages in the finished interior PDF:
| Interior page count | Inside margin (gutter) |
|---|---|
| 24–150 pages | 0.375 in |
| 151–300 pages | 0.5 in |
| 301–500 pages | 0.625 in |
| 501–700 pages | 0.75 in |
| 701–828 pages | 0.875 in |
CrayonMill's page-building tools cover the first two bands (24–300 interior pages); a book planned for a thicker interior needs a different workflow for now.
Interior pages: 80 · within the supported range (24–300) · gutter 0.375 in
Why "interior page count" is not "art page count"
This is where gutter mistakes happen. A coloring book generated single-sided — one drawing per sheet, blank back — has an interior PDF with twice as many pages as it has drawings, because the blank backs count. 76 drawings become a 152-page interior. That crosses from the 24–150 band into the 151–300 band, which changes the gutter from 0.375 in to 0.5 in. Counting art pages instead of interior pages is the single most common way a coloring book ends up with the wrong gutter set.
Double-sided books (front and back both carry art) don't have this doubling — interior page count equals art page count there, so the band is easier to read off directly.
What the gutter actually protects
The gutter is extra white space added to the inside edge of every page, next to where the book is glued or sewn into its cover. Without it, art placed close to the spine can curl into the binding once the book is trimmed and bound, making that part of the drawing hard to see or color. The gutter alternates sides through the book — right-hand (recto) pages get it on the left, left-hand (verso) pages get it on the right — so content needs to be kept clear of whichever edge is next to the spine on that particular page, not just one fixed edge throughout.
How this fits with the outer margin
The gutter is one of four margins on a page — top, bottom, outer edge, and the inside/gutter edge — and it's the only one that changes with page count. The three outer margins follow a separate, page-count-independent minimum (see the safe margins guide). A page that respects the outer margins but ignores the gutter band for its actual interior page count can still fail review, because the two checks are independent.
Getting it right without doing the math
Because the gutter depends on interior page count and interior page count depends on whether the book is single- or double-sided, it's easy to set the wrong value by working from the art page count instead. CrayonMill's PDF builder reads the interior page count directly from the generated pages and sets the gutter automatically, so this is not a value authors need to look up or type in themselves.
Sources
Last verified 2026-09-04. Updated 2026-09-04.