How to format a paperback for Amazon KDP
Updated November 2026
KDP rejects paperback files for small, fixable reasons: margins that are too narrow, fonts that aren't embedded, or a cover that doesn't match the spine width. Here are the rules that matter.
Pick a trim size
6 x 9 inches is the most common size for novels in the US. 5.5 x 8.5 and 5 x 8 are popular for shorter fiction. Choose the trim size before you format, because it changes your page count, your spine and your cover.
Margins and gutter
The gutter is the inside margin, next to the binding. KDP's minimum depends on page count:
| Pages | Minimum inside (gutter) margin |
|---|---|
| 24 to 150 | 0.375 in |
| 151 to 300 | 0.5 in |
| 301 to 500 | 0.625 in |
| 501 to 700 | 0.75 in |
| 701 to 828 | 0.875 in |
Outside, top and bottom margins must be at least 0.25 in without bleed. Most professional books use more, around 0.5 to 0.75 in, so the page doesn't feel crowded. Margins should mirror: left pages and right pages have the gutter on opposite sides.
Fonts
Every font must be embedded in the PDF. Use a book serif for body text at 10.5 to 12 point with comfortable line spacing. Start each chapter on a new page, and add a title page, a copyright page and page numbers.
Spine width
Spine width depends on page count and paper. For black and white interiors, KDP uses about 0.002252 in per page on white paper and 0.0025 in per page on cream paper. A 300-page book on cream paper has a spine of about 0.75 in. KDP only allows text on the spine for books with more than 79 pages.
Wrap cover size
The paperback cover is one PDF: back cover, spine and front cover side by side, with 0.125 in of bleed on every outside edge. Width = 0.125 + trim width + spine + trim width + 0.125. Height = 0.125 + trim height + 0.125. Leave a 2 x 1.2 in area clear on the lower right of the back cover for the barcode KDP adds.
The fast way
Authora's Print Pack builds both files from your book: a typeset interior PDF in your trim size with KDP-correct margins, embedded fonts, title, copyright, contents and dedication pages, drop capitals and page numbers, plus a full wrap cover with the spine measured to your exact page count. It costs $14.99 per book and works with books you import from Word too.
Questions
What is the most common paperback size on KDP?
6 x 9 inches is the most common trim size for novels sold in the US.
How wide is the spine on a KDP paperback?
About 0.002252 inches per page on white paper and 0.0025 inches per page on cream paper for black and white interiors.
Why did KDP reject my paperback interior?
The most common reasons are margins below the minimum for your page count, fonts that aren't embedded, and a page size that doesn't match the trim size you chose.
Try it on your own book
Authora plans, writes and edits your book in the style you choose, then makes the cover, the Kindle e-book and the print-ready paperback. The free trial includes 10,000 words, no card needed.