How to format a book for KDP: trim, margins, matter, and the two files you need

Pick your trim size first — everything else depends on it

Trim size is the physical dimension of the printed page, and it's the first decision because margins, page count, spine width, and your cover dimensions all derive from it. For fiction, 6 x 9 inches is the workhorse — it's the size readers expect for a trade paperback and it keeps page count (and therefore printing cost) down for longer books. 5 x 8 and 5.25 x 8 read slightly more 'mass market' and suit shorter novels.

Page count matters commercially, not just aesthetically: KDP's print cost is driven by pages, and print cost comes out of your royalty. A 100,000-word novel at 6 x 9 lands somewhere around 350–400 pages depending on font and leading; the same book at 5 x 8 runs meaningfully longer and costs more to print. Pick the trim, then set type to it — not the other way around.

Margins and the gutter — where most print rejections happen

Print margins aren't symmetric. The inside margin — the gutter — must be larger than the outside, because the binding swallows part of the inner page, and how much it swallows grows with page count. KDP publishes minimum gutter requirements by page count; a 400-page book needs more inside margin than a 200-page one. Set your document to mirrored margins so left and right pages gutter correctly.

The other print-only rules: no content in the outer 0.25-inch safety zone, embed every font in the PDF, and if any image or design element is meant to run to the page edge, you need bleed — the element extends past trim and the page size grows accordingly. Miss any of these and KDP's automated preflight flags the file before a human ever sees it.

• Gutter scales with page count — check KDP's table for your final count, not your draft's.
• Mirrored margins, so inside/outside apply correctly to facing pages.
• All fonts embedded in the PDF — 'it looked fine on my machine' is a font-embedding bug.
• Bleed only if elements run to the edge; most text-only novels don't need it.

Front matter, back matter, and what order they go in

There's a conventional order readers and retailers expect. Front matter: title page, copyright page (with your ISBN if you have one and the all-important 'this is a work of fiction' notice), optional dedication, optional table of contents — genre fiction paperbacks often skip the printed ToC, but the ebook must have a navigational one. Then the story.

Back matter is where indie authors leave money on the table. An 'also by' page, a newsletter signup, and — the single highest-value page in the book — a note asking for a review, placed right where the reader finishes. In the ebook you can link these directly; in print they carry the URL. Keep back matter short: two or three pages that each do one job.

EPUB vs print PDF: two files, two philosophies

The paperback PDF is fixed: you decide where every line breaks, and the file is a photograph of those decisions. The EPUB is the opposite — reflowable by design, because the reader controls font, size, and margins on their device. This is why exporting your print-formatted PDF 'as the ebook' fails: hard page breaks, fixed fonts, and absolute positioning are print virtues and ebook defects. The EPUB needs semantic structure — real heading styles for chapters, a navigation document, no manual tab-and-space typesetting.

This is also what EPUBCheck validation means when you see it mentioned: EPUBCheck is the W3C-maintained validator that confirms your EPUB is structurally sound — valid packaging, working navigation, no broken internal links — before a store's ingestion pipeline finds out the hard way. Passing EPUBCheck doesn't guarantee your book is pretty, but failing it predicts rejections and rendering bugs across devices.

You can absolutely do all of this by hand — authors have for years, with a word processor for the PDF and Calibre or similar for the EPUB. If you'd rather not, this is the job Scribegrove's Publishing Studio does: a KDP-ready print PDF and a W3C EPUBCheck-validated EPUB 3.3 with ONIX 3.0 metadata, generated from the manuscript you already have, plus submission wizards that walk you through KDP, Draft2Digital, IngramSpark, Apple, and Kobo. It's an add-on at $14.99/month, or bundled into the Max tier — honest math: if you publish once a year, a single month of the add-on around launch may be all you need.