Best Book Formatting Software in 2026,
Including the AI Formatters

The picks at a glance

Ordered by the situations most authors are in, not by one score. Prices are each vendor's own, in US dollars, checked 9 October 2026.

What book formatting software actually has to do

A manuscript in a word processor is one long scroll of text. A book is two different products made from it, and a formatter's job is to make both without you setting every page by hand.

The paperback is a fixed layout. Every page has a set size (the trim), a wider margin on the spine side so words do not disappear into the binding, running headers or footers, page numbers that start in the right place, chapters that open on a fresh page, and fonts embedded in the PDF so the printer cannot swap them. On Amazon KDP, the inside margin grows with the page count, because a thicker book curves more at the spine:

The outside margin is at least 0.25 inch without bleed and 0.375 inch with it. Bleed, for pictures that run off the page edge, is 0.125 inch, and even one bleed page means the whole interior is set up with bleed and uploaded as a PDF. The regular KDP trims are 5 x 8, 5.06 x 7.81, 5.25 x 8, 5.5 x 8.5 and 6 x 9 inches; larger sizes up to 8.5 x 11 and A4 cost more to print. All of this is from KDP's trim, bleed and margins page, checked 9 October 2026. Our KDP paperback guide walks through the upload itself.

The ebook is a reflowable file. There are no pages: the text reflows to fit a phone, a tablet or an e-reader at whatever font size the reader picks. What matters is a linked table of contents, clean chapter breaks, images that scale, and a file the store accepts (ebook formats explained). KDP takes DOCX, EPUB, KPF (from Kindle Create), HTML, RTF and TXT for Kindle ebooks, and PDF only for some languages. It no longer takes MOBI: reflowable MOBI ended on 1 August 2021 and fixed-layout MOBI on 18 March 2025. If a tool still advertises MOBI as its Kindle format, that is a tool that has not kept up.

The cover is a third file (cover design guide). For a paperback, KDP wants one PDF with the back, the spine and the front, plus 0.125 inch bleed on every edge. The spine width comes from your page count and paper: 0.002252 inch a page on white paper and 0.0025 inch on cream, so a 284-page book on white paper has a spine of about 0.64 inch. KDP's help is inconsistent on the exact threshold for spine text (it says both "at least 79" and "more than 79" pages), so the safe rule is spine text from about 80 pages. Most formatters do not make this file at all.

Book formatting software compared: KDP fit and covers

"Print PDF" means the tool exports a paperback interior with trim and margins set; "Wrap cover" means it makes the full back, spine and front cover file KDP asks for.

AI book formatting software: what it does and does not do yet

Search "best book formatting software" and the roundups list Vellum, Atticus and Kindle Create, none of which has AI. Meanwhile a new group of tools uses AI to write or rebuild the book and then lays it out. They work differently, and it helps to know which kind you are looking at.

Template formatters (Vellum, Atticus, Kindle Create, Reedsy) take a finished manuscript and apply a design to it. You choose, the tool applies, and you can adjust every chapter opening by hand. Their strength is typographic depth: hundreds of fonts, theme builders, footnotes, large print.

AI book tools that format start earlier. Inkfluence AI drafts the outline and chapters with you (or imports your draft and edits it), then formats the book in one of five styles and builds the KDP files, including the wrap cover. Built&Written turns a coach's notes, posts or transcripts into a KDP book on a subscription ($19, $49 or $99 a month; EPUB and DOCX only from the $49 plan). BookFoundry sells AI-written books from $14.99 each on credits that are non-refundable once used, with DOCX, EPUB and print PDF from every book, though it does not publish its trim list.

AI inside general tools is a third kind. Word has Copilot, Google Docs has Gemini on paid plans, InDesign has generative image tools and text rewriting, and Calibre added an optional assistant that uses your own AI account. All of them help with words or pictures. None of them lays out a book for you.

The honest trade-off: AI formatters save the most time when the book is not finished or you have never formatted one, and they give you the cover and KDP files without a second tool. Template formatters still win when you want to hand-tune a finished novel's typography page by page. You can also draft with AI and format in Atticus or Vellum; our Inkfluence vs Atticus and Inkfluence vs Vellum comparisons cover how to move a book between them.

The best free book formatting software

Free tools have caught up for simple books. Here is what each free option gives you, and where it stops.

For a text-only novel going only to Amazon, Kindle Create is genuinely enough. For a book you want in every store (going wide), Reedsy or Draft2Digital. For anything with images, Affinity, now that it costs nothing. If you need to check the money side first, our free KDP tools work out print cost and royalty by trim and page count, and the royalty calculator compares KDP with five other stores.

How to format a book for KDP, with any of these tools

The steps are the same whichever formatter you use. The tools differ in how many of them they do for you.

1. 1

   Finish and clean the manuscript

   Use heading styles for chapter titles (Heading 1), remove manual tabs and double spaces, and decide your front matter: title page, copyright page, dedication, contents.

2. 2

   Pick the trim size first

   6 x 9 inches is the common trade size for non-fiction and many novels; 5.5 x 8.5 and 5 x 8 suit shorter fiction. Your page count, and so your margins and spine, follow from it.

3. 3

   Import into your formatter and choose a style

   Bring in the DOCX, pick a theme or style, and set chapter openings, scene breaks and drop caps once for the whole book.

4. 4

   Set margins for your page count

   Check the inside margin against KDP's table (0.5 inch for 151 to 300 pages). Most formatters set it for you; in Word you set mirror margins yourself.

5. 5

   Export two files

   A print PDF at your trim size with fonts embedded for the paperback, and an EPUB or DOCX for the Kindle ebook.

6. 6

   Make the full wrap cover

   Back, spine and front in one PDF with 0.125 inch bleed, the spine width set from your final page count and paper. Add spine text only from about 80 pages.

7. 7

   Upload, preview and order a proof

   Use KDP's print previewer to catch margin and bleed errors, then order a proof copy and read it with a pencil before you publish.

For the publishing side after the files are ready, see self-publishing on Amazon KDP, and if AI wrote any part of the book, KDP's AI disclosure rules and how to publish an AI-assisted book on KDP.

Book formatting software FAQ