A paperback is a physical object, and the printer has rules about it that an ebook does not. Most rejected or disappointing print files come from the same handful of decisions: the page size, the margins, whether images run to the edge, and how the cover is built. This guide explains each one so you know what to ask for, or what to check, before you upload.
Start with the trim size
Trim size is the finished page size after the book is cut. Pick it before you format anything, because the margins, the page count and the cover all depend on it. Look at published books in your genre on your own shelf: novels, memoirs and workbooks tend to settle on different sizes for good reasons, and readers notice when a book feels wrong in the hand.
Amazon KDP lists the trim sizes it supports and which are available for which paper and ink choices. Check that list when you decide, because it changes over time.
Margins, and why the inside one is wider
Every page needs a safe margin so text is never cut off or lost in the fold. The inside margin, next to the spine, must be wider than the outside one because the pages curve into the binding. As a book gets thicker, it needs more room on that inside edge.
KDP publishes its minimum margins for each page count range. Treat those as a floor, not a target. Comfortable margins make a book look professional, and cramped ones are one of the quickest ways a print book looks self-published in the worst sense.
- Set the inside (gutter) margin larger than the outside margin.
- Leave space at the top and bottom for page numbers and running heads.
- Keep every word, and anything important in an image, inside the safe area.
Bleed: only when something touches the edge
Bleed is extra image area that extends past the trim line, so that when the page is cut there is no thin white edge. You need it only when a picture, colour or pattern runs right to the edge of the page. A plain black-text-on-white novel does not need bleed.
If you do use it, KDP specifies how far the image must extend. Build it into the file from the start rather than stretching an image later.
The interior file
Print interiors are normally uploaded as a PDF with fonts embedded, so the pages look the same on the printer's machines as on yours. Chapter openings usually start on a right-hand page, which is why paperbacks have blank pages here and there. Page numbers should start where the story starts, not on the title page.
Use real paragraph and heading styles in your layout software rather than typing spaces and returns to push text around. It keeps the pages consistent and makes later corrections easy.
The cover is one wraparound file
A paperback cover is a single flat file with the back cover, the spine and the front cover side by side. The width of the spine depends on the page count and the paper type, so the cover cannot be finished until the interior is final. KDP provides a cover calculator and a template for this.
If your book is thin, the spine may be too narrow to carry text. If you add or remove pages after the cover is made, the spine changes, and the cover needs to be rebuilt.
Check before you publish
Use KDP's online previewer to look at every page, then order a printed proof copy. A proof tells you things a screen never will: whether the margins feel right, whether the cover colours look as intended, and whether the spine text lines up. It is a small cost compared with a flawed print run you have already announced.
If you would rather not do this yourself, Marlowe's paperback formatting service prepares the interior and the cover files to the printer's requirements.