Calculate the gutter before the binding swallows your text.
Enter final page count, trim, and bleed. The calculator returns Amazon KDP’s current minimum margins, a more comfortable design starting point, millimeters, and the resulting text-block dimensions.
Use the final formatted page count, including front and back matter.
301–500 page bracket
Minimum means the file can meet this margin rule. It does not guarantee a comfortable or well-proportioned page.
This is a neutral starting point, not a platform requirement. Refine it with the actual typeface, line length, headers, folios, binding, genre, and proof copy.
4.25 × 7.00 in text block
Recommended margins use 77% of page width and 82% of page height.
How the calculator works
Amazon KDP currently sets the minimum inside margin by final page count. Books from 24–150 pages need at least 0.375 inches, 151–300 need 0.5, 301–500 need 0.625, 501–700 need 0.75, and 701–828 need 0.875. Outside, top, and bottom margins must be at least 0.25 inches without bleed or 0.375 inches with bleed.
The calculator applies that official table exactly for the “technical minimum.” The second result deliberately adds room: 0.125 inches to the minimum gutter, at least 0.5 outside, and 0.75 top and bottom. Those are design starting points only. A book with running heads may need more top space; a folio and footnotes may need more bottom space; a thick binding or very compact trim may need a wider apparent gutter.
Inside, outside, gutter, and bleed
Book pages should use inside and outside margins because the bound edge alternates. On a right-hand page, the inside margin is on the left. On a left-hand page, it is on the right. Ordinary “left” and “right” margins cannot express this correctly unless the application mirrors them.
Some software exposes both an inside margin and a separate gutter field. KDP refers to the inside margin as the gutter, so follow the application’s own field semantics and confirm the resulting PDF rather than assuming two labels mean two independent requirements. The PDF’s actual live area is what matters.
Bleed is the extra image area trimmed away when art reaches the edge. It changes the PDF page dimensions and raises the minimum safety margin on the outside edges. It does not mean ordinary body text should move closer to the cut.
Why a minimum margin can still look wrong
A platform checks whether content stays beyond a technical safety line. It does not evaluate whether the spread feels balanced or the line length is comfortable. At a 6 × 9 trim, minimum side margins can produce a very wide text block. On a 5 × 8 book with hundreds of pages, the same values may feel crowded near the binding.
Judge the page as a relationship among trim, typeface, size, leading, line length, page count, and paper. Print representative spreads at 100 percent and order a proof. If readers have to force the book open or the outside edge feels cramped, passing preflight has not solved the design problem.
Use the final page count
Page count is not word count divided by a universal constant. Trim, typeface, type size, line spacing, chapter starts, front matter, images, and blank pages all change it. Format the complete interior, then use the final count to confirm the margin bracket and size the cover spine.
If changing the gutter pushes the book into the next page bracket, calculate again. Very long books can enter a feedback loop where more inside space increases pages, and the higher page count requires more inside space. A book-aware typesetting tool recomposes the entire interior so the result can be checked rather than estimated.
Margin setup checklist
- Choose the final trim before setting margins.
- Use the formatted page count, including front and back matter.
- Confirm whether the edition has bleed.
- Use mirrored inside and outside margins.
- Meet the current printer minimum, then evaluate a larger design margin.
- Leave room for running heads, folios, footnotes, and special content.
- Check line length after the live area changes.
- Inspect left/right spreads, chapter openings, and the longest pages.
- Verify the exported PDF dimensions and live area.
- Review the retailer preview and a physical proof.
Before you export the interior
What is the gutter margin of a book?
The gutter is the inside margin beside the binding. It needs enough space to keep text readable when the book is opened. KDP increases its minimum inside margin as page count rises.
Are KDP minimum margins good book-design margins?
They are technical minimums, not a universal design recommendation. A professional interior often uses more outside, top, or bottom space based on trim, type, page count, and reading comfort.
Do margins change when a book has bleed?
Yes. KDP currently requires at least 0.375 inches for top, bottom, and outside margins when content bleeds, versus at least 0.25 inches without bleed. The inside minimum still depends on page count.
Should left and right margins be the same?
A bound book should use mirrored inside and outside margins, not ordinary left and right margins. The inside edge alternates across facing pages.
Does trim size change the KDP minimum gutter?
The current KDP gutter table is based on page count rather than trim. Trim still changes the resulting text-block width and the visual proportion of the margins.