Gutter Margin Calculator
The inside margin your page count needs
The gutter is the inside margin next to the spine, and it has to grow with your page count, because a thicker book curves more at the binding. Set it too small and readers lose words into the fold. Enter your page count and get the gutter margin KDP recommends.
What is a gutter margin?
The gutter is the extra inside margin along the spine edge of each page, added so that text is not swallowed by the binding when the book is bound. It is separate from the outside margins, and unlike them it must increase as the book gets thicker, because more pages mean a tighter curve at the spine.
How big should the inside margin be?
On Amazon KDP the recommended gutter grows in steps: about 0.375 inches up to 150 pages, 0.5 inches to 300 pages, 0.625 inches to 500 pages, 0.75 inches to 700 pages, and 0.875 inches beyond that. Outside, top and bottom margins can stay around 0.25 to 0.5 inches with bleed considered separately.
What happens if the gutter is too small?
Text near the spine bends into the binding and becomes hard or impossible to read, especially in the middle of a thick book. It is one of the most common print rejections and reader complaints, and it is entirely avoidable by sizing the gutter to the page count before you export.
Frequently asked questions
What is a gutter margin?
The extra inside margin along the spine, added so text is not lost in the binding. It grows with page count.
How big should the inside margin be on KDP?
Roughly 0.375 in up to 150 pages, 0.5 in to 300, 0.625 in to 500, 0.75 in to 700, and 0.875 in beyond.
What if my gutter is too small?
Text bends into the binding and becomes unreadable near the spine, a common print rejection that is easy to avoid.
Is the gutter the same as the outside margin?
No. The gutter is the inside (spine) margin and must grow with page count; outside margins stay roughly constant.