Self-Publishing File Formats: Amazon, Apple, Google, and More

The file format you upload to a self-publishing platform determines how your book looks on every device your readers own. Get it wrong and you're dealing with missing cover images, broken table of contents, scrambled formatting, and one-star reviews mentioning "terrible formatting" before anyone reaches your actual content.

The good news: the format ecosystem has consolidated. EPUB is accepted everywhere. Amazon's insistence on proprietary formats has softened — KDP now prefers EPUB over their own formats. The bad news: each platform has specific requirements for cover dimensions, interior formatting, metadata, and quality checks that aren't consistent across platforms. This guide covers every major self-publishing platform's requirements in detail.

Platform Format Requirements at a Glance

* Amazon deprecated MOBI uploads but some legacy documentation still references it. Use EPUB.

Amazon KDP (Kindle Direct Publishing)

Amazon is the largest ebook retailer, and KDP is the gateway. As of 2026, EPUB is their recommended upload format, replacing years of MOBI/AZW3 guidance.

Accepted Formats and Conversion Pipeline

KDP accepts EPUB, DOCX, KPF (Kindle Package Format from Kindle Create), and PDF. Regardless of what you upload, Amazon converts it internally to KFX for delivery to devices with enhanced typesetting, and to AZW3 for older devices. Your source file is a starting point — you never control the final delivery format.

EPUB gives the most predictable results because KDP's conversion pipeline was designed around HTML-based content. Well-structured EPUB with clean CSS translates cleanly to KFX. DOCX works but Amazon's interpretation of Word formatting can produce surprises — paragraph spacing, indentation, and font sizing may not match what you see in Word. PDF uploads create "print replica" Kindle books with fixed pages, not reflowable ebooks — appropriate for textbooks and technical manuals, not novels. KPF is the output of Kindle Create, Amazon's free formatting tool, and gives you the most control over Kindle-specific features.

Cover Image Specifications

KDP cover requirements are the most specific of any platform:

• Dimensions: Minimum 625x1000 pixels. Recommended 2560x1600 pixels. Maximum 10,000 pixels on the longest side
• Aspect ratio: 1.6:1 (height:width). A 2560x1600 cover fits perfectly
• File format: JPEG or TIFF. No PNG (Amazon rejects it). RGB color space only — CMYK covers are rejected
• File size: Under 50MB
• DPI: At least 300 DPI for the cover image. Lower DPI results in a quality warning

The cover is uploaded separately from the manuscript on KDP, not embedded in the EPUB. However, the EPUB should also contain the cover image internally (referenced in the OPF with properties="cover-image") for the preview and Look Inside feature. If the embedded cover and uploaded cover don't match, the uploaded cover takes priority on the store page.

Interior Formatting Guidelines

KDP's content guidelines for interior formatting:

• Images: 300 DPI minimum for images expected to display full-width. RGB color space. JPEG or PNG. Total file size for the manuscript (including images) should stay under 650MB
• Tables: Kindle renders tables poorly on small screens. Avoid complex tables with many columns. Simple two or three-column tables work; anything wider gets horizontally scrollable or truncated
• Fonts: Embedded fonts in EPUB are preserved in the KFX conversion. But Kindle users can override fonts, so don't rely on a specific typeface for meaning (e.g., using Courier for code is fine; using a decorative font for chapter titles is risky)
• Page breaks: Use CSS page-break-before: always to force chapter breaks. KDP respects these. Without them, chapters may run together
• Table of contents: Required. KDP checks for a functional TOC (clickable links that navigate to chapters). A missing or broken TOC triggers a quality warning and may block publication

Apple Books (Formerly iBooks)

Apple Books has the strictest format requirements but also the best rendering engine for well-crafted EPUBs.

EPUB3 Requirement

Apple Books requires EPUB 3. EPUB 2 files are accepted but may render inconsistently. Apple is the only major platform that fully supports EPUB3 features: media overlays (synchronized audio), JavaScript in content documents, MathML rendering, and SVG interactivity. If you're building read-along children's books with audio narration, Apple Books is the primary distribution channel.

Apple also accepts iBooks Author (.iba) files — their proprietary format for interactive textbooks and multi-touch books. iBooks Author was discontinued in 2020, replaced by Pages (which exports to EPUB). Legacy .iba files still work on Apple Books but new content should use EPUB3.

Submission via Apple Books for Authors

Apple Books for Authors (formerly iTunes Connect for Books) is the submission portal. Upload EPUB3, set pricing, select territories, and submit for review. Apple has a review process — not as rigorous as App Store review, but they check for quality issues: broken TOC, missing cover, formatting errors, and content policy violations. Review typically takes 24-48 hours.

Cover requirements: minimum 1400 pixels on the shorter side, 1.333:1 aspect ratio (portrait), JPEG or PNG, RGB. Apple accepts PNG covers (unlike Amazon). Interior images have no strict size limit, but Apple recommends keeping the total EPUB under 2GB. The asset guide specifies RGB color space for all images.

Google Play Books

Google Play Books accepts EPUB and PDF with relatively relaxed requirements compared to Amazon and Apple.

Format and Quality Requirements

Upload via the Google Play Books Partner Center. EPUB is preferred for reflowable content, PDF for fixed-layout content. Google's epubcheck validation is strict — any epubcheck error will block your upload. Common blockers: missing required metadata, invalid XHTML, and referenced resources not found.

Cover image: minimum 640 pixels on the shortest side, JPEG or PNG, no text in the bottom 20% of the cover (Google overlays price and "Sample" badges there). Google extracts the cover from the EPUB — there's no separate cover upload. Make sure your EPUB embeds a high-quality cover image.

Google Play Books' renderer handles EPUB3 features well: embedded fonts, CSS3, SVG. It doesn't support JavaScript or media overlays. For fixed-layout content, Google recommends PDF over EPUB3 FXL, citing better rendering consistency.

Kobo Writing Life

Kobo is the second-largest dedicated ebook retailer after Amazon and the dominant platform in Canada, Japan, and parts of Europe.

Format Requirements

Kobo Writing Life accepts EPUB and DOCX. EPUB is strongly preferred — DOCX uploads go through Kobo's conversion pipeline, which can produce inconsistent results. Kobo validates EPUBs with epubcheck and rejects files with errors.

Kobo supports both EPUB 2 and EPUB 3. Their Kobo e-readers have excellent EPUB rendering including embedded fonts, CSS3, and fixed-layout EPUB. Kobo's reader app is one of the best for respecting author CSS while still allowing user customization.

Cover requirements: minimum 1400x1873 pixels (3:4 ratio), JPEG, RGB. Kobo extracts the cover from the EPUB. Interior image limit: 5MB per individual image. Total EPUB size should stay under 100MB for reliable processing. Convert DOCX to EPUB before uploading for the best results.

Aggregators: Draft2Digital and Smashwords

Aggregators distribute your book to multiple retailers from a single upload — a convenience layer that saves uploading separately to each platform.

Draft2Digital

Draft2Digital (D2D) distributes to Apple Books, Kobo, Barnes & Noble, Scribd, libraries (via OverDrive, hoopla), and more. They accept DOCX and EPUB. Upload DOCX and D2D's conversion engine produces EPUB with their formatting templates, or upload your own pre-made EPUB for direct distribution.

D2D's DOCX-to-EPUB conversion is genuinely good — better than Smashwords' Meatgrinder (see below). They handle chapter detection, TOC generation, and front/back matter formatting automatically. But if you care about exact formatting control, create your EPUB externally and upload it directly. D2D distributes your file as-is to retailers.

Smashwords

Smashwords (now owned by Draft2Digital) uses the "Meatgrinder" — their DOCX-to-EPUB conversion engine. It's the oldest and most temperamental conversion pipeline in self-publishing. Smashwords accepts only DOCX. No EPUB, no PDF, no HTML.

The Meatgrinder requires specific DOCX formatting: use Word's built-in styles (Heading 1, Heading 2, Normal) rather than manual formatting, insert page breaks via Word's page break feature (not multiple blank lines), use Times New Roman or Georgia as the base font, and include a specific front matter structure. Deviating from these requirements produces formatting errors.

Smashwords' "Premium Catalog" distribution (to Apple, Kobo, B&N) requires passing an additional formatting review. Common rejection reasons: NCX TOC issues, insufficient image resolution, and formatting artifacts from Word. For authors who want direct EPUB control, Draft2Digital's EPUB upload path is strictly superior.

ISBN: When You Need One, When You Don't

An ISBN (International Standard Book Number) uniquely identifies a specific edition of a book. Each format (hardcover, paperback, EPUB, audiobook) needs its own ISBN.

Platform ISBN Requirements

Amazon KDP: ISBN not required. Amazon assigns a free ASIN (Amazon Standard Identification Number) to every KDP book. You can add your own ISBN if you have one, but it's optional. Apple Books: ISBN required for distribution. Apple provides free ISBNs to books published through Apple Books for Authors. Google Play: ISBN required. Must be a valid ISBN-13. Kobo: ISBN required for most territories. Kobo provides free ISBNs in some countries. Draft2Digital: Provides free ISBNs or accepts your own. Smashwords: Provides free ISBNs.

If you buy your own ISBN (from Bowker in the US — $125 for one, $295 for 10, $575 for 100), you control the publisher imprint. If you use a free ISBN from a platform, that platform is listed as the publisher of record. For serious self-publishers building a brand, owning your ISBNs matters. For casual publishing, free ISBNs from platforms are fine.

The One-File Workflow: EPUB for Everything

The practical workflow for multi-platform self-publishing:

1. Create your EPUB — Start from DOCX, Markdown, or HTML. Use Calibre, Sigil, or Pandoc to produce a clean EPUB3 with embedded cover, functional TOC, complete metadata, and proper CSS. Convert DOCX to EPUB as a starting point, then refine in Sigil
2. Validate — Run epubcheck. Fix all errors and warnings. Every platform runs epubcheck; failing it means rejection
3. Test on devices — Open in Apple Books, Calibre, and Kindle Previewer. Check cover, TOC, chapter breaks, images, and formatting across renderers
4. Upload everywhere — Amazon KDP (EPUB), Apple Books (EPUB3), Google Play (EPUB), Kobo (EPUB), Draft2Digital (EPUB). One file, five platforms
5. Covers — Upload the same 2560x1600 cover everywhere. Amazon has the largest dimension requirement; meeting it covers all platforms

This workflow produces consistent results across all platforms. The only per-platform variation is Amazon's KFX conversion, which you can preview with Kindle Previewer 3 before publishing.

Self-publishing format requirements have converged on EPUB. The era of needing different files for different platforms is over. Create one well-crafted EPUB3, validate it with epubcheck, and upload it everywhere. The platforms handle their internal conversions.

The effort that matters isn't in format conversion — it's in the EPUB creation. Clean HTML structure, proper CSS, embedded cover image, complete metadata, and a functional table of contents make the difference between a professional-looking ebook and one that gets complaints about formatting. Invest time in the EPUB, and the platform distribution is straightforward.