How to Format a Book for Self-Publishing in 2026

eBooks are reflowable documents. Unlike print, the reader controls the font size, font type, and line spacing — your formatting defines the structure, not the final appearance. Understanding this distinction is the foundation of correct eBook formatting.

File Types: EPUB, MOBI, and KPF

Reflowable vs. Fixed Layout

Reflowable layout is the default for novels, narrative nonfiction, and most standard text-based books. The content reflows to fit any screen size — a reader on a phone sees the same content as one on a Kindle Oasis, just formatted differently. Use reflowable for all standard prose.

Fixed layout preserves exact page positioning — every element stays exactly where you put it. Required for children's picture books, cookbooks with specific visual layouts, graphic novels, and heavily illustrated nonfiction where position relative to images matters. Fixed layout does not scale gracefully to small screens and is not searchable in the same way. Only use it when the visual layout is inseparable from the content.

Metadata Requirements

Every EPUB must contain metadata embedded in its package file. Platforms read this metadata to categorize and display your book correctly. Required metadata:

• Title — must match your distribution title exactly
• Author — full name as it appears on your cover and catalog listing
• ISBN — if you're using a purchased ISBN (not required for all platforms, but required for wide retail distribution)
• Language — ISO 639 language code (e.g., "en" for English)
• Publisher — your name or your publishing imprint name
• Description — your book blurb (used by some platforms in the catalog)
• Cover image — embedded in the EPUB; minimum 1400px on the shortest side, 2560px recommended

Formatting software like Vellum and Atticus fills in most metadata through a form during the export process. If you're formatting manually in Sigil or with Calibre, you'll set these fields directly in the metadata editor.

Print formatting is more technically demanding than eBook formatting. You're producing a fixed PDF that a printer will use to manufacture physical books — every measurement must be exact. Get this wrong and you'll receive a rejection with a cryptic technical error, or worse, print proof copies with misaligned pages.

Trim Sizes

Trim size is the finished size of the printed book. Choosing a non-standard trim size increases per-unit printing costs and may limit distribution availability. These are the most common options:

Margins, Gutters, and Bleed

ISBN Barcode Placement

The ISBN barcode must appear on the back cover, bottom right, within a clear white or light-background zone. KDP and IngramSpark will add the barcode automatically if you provide your ISBN — they handle placement. If you're designing a cover independently (e.g., using a cover designer who provides a print-ready file), ensure the barcode zone is reserved: a white rectangle approximately 1.5" × 1" in the lower-right quadrant of the back cover, with at least 0.25" of clear space on all sides.

If you're using a KDP free ISBN, the barcode is placed automatically and you don't control the placement. With a purchased Bowker ISBN, you provide the number to your cover designer or the platform's cover tool. For a full breakdown of ISBN costs and when to buy your own, see our self-publishing cost guide.

Five tools dominate book formatting in 2026. Here's how they compare across the dimensions that matter for indie authors — pricing, platform support, learning curve, and output quality. For a broader look at self-publishing tools, see our complete self-publishing tools comparison.

The recommendation for most indie authors: Vellum if you're on Mac and planning a series; Atticus if you're on Windows or want a lower cost entry point. Both produce professional-quality output that matches traditionally published books. Reedsy is fine for a single simple title. Calibre is for conversion and library management, not authoring. InDesign is only worth the learning curve and subscription cost if you're producing heavily illustrated nonfiction where layout complexity is genuinely beyond what the dedicated tools handle.

Note that hiring a professional formatter ($75–$350) is a legitimate alternative — especially for a single book where the one-time software cost doesn't justify itself. For the pricing breakdown, see our self-publishing cost breakdown.

KDP accepts eBook and print uploads. eBook accepts EPUB, MOBI, DOCX, and KPF. Print accepts PDF only. The process is different for each — here's what to do.

IngramSpark is the path to physical bookstore and library distribution. Its technical requirements are stricter than KDP's — but if you're serious about print distribution beyond Amazon, this is the platform you need. For context on why IngramSpark matters alongside KDP, see our step-by-step self-publishing guide.

These are the formatting errors that actually cause upload rejections or visible production problems — not theoretical edge cases, but the mistakes that show up repeatedly in author communities and support queues.

Formatting a book for both eBook and print across multiple platforms involves more moving parts than most authors anticipate: different file versions for KDP vs. IngramSpark, separate cover files for print vs. digital, upload queues with different review windows, proof copy tracking, and correction rounds when something doesn't pass validation.

BoomerangOS gives you a formatting checklist as part of your publishing pipeline — one view that tracks the status of every format (eBook EPUB, KDP print PDF, IngramSpark interior, IngramSpark cover), every upload submission, every proof order, and every platform approval. When you have three formats in flight across two platforms, knowing which one is waiting for your action vs. waiting for platform review is the difference between a tight launch timeline and a launch that slips two weeks.

Formatting is one stage in a larger sequence. Once your files are approved, the next phase is distribution setup, pricing, pre-order configuration, and launch marketing — all of which require their own tracking. Our book marketing strategies guide covers what happens after the files go live. And if you're comparing whether self-publishing's formatting requirements are worth the tradeoff vs. traditional publishing, the self-publishing vs. traditional comparison puts it in full context.

Formatting doesn't have to be the thing that delays your launch. The authors who get it right the first time follow a consistent pre-upload checklist:

• eBook: EPUB 3 file, embedded metadata, functional TOC, cover at 2560px, tested in Kindle Previewer and Apple Books preview
• KDP print: PDF with embedded fonts, correct trim size, gutter matched to page count, cover with spine width from KDP calculator
• IngramSpark print: PDF/X-1a or X-4 interior, 300 DPI images, cover with 0.125" bleed and barcode zone reserved, proof copy ordered before going live
• Both platforms: ISBNs registered and entered, pricing set and profitability confirmed, metadata consistent across all platform listings

The right formatting tool makes this manageable — Vellum or Atticus will handle most of the technical complexity automatically. What they can't do is track your launch timeline, manage your contractor relationships, or keep your platform approval status in one place. That's what BoomerangOS is for.

If you're not yet at the formatting stage, the complete publishing checklist shows where formatting sits in the full launch sequence — and what comes before and after it.