Kindle Ebook File Types: EPUB, MOBI, KFX and What KDP Actually Accepts

Authors preparing a KDP ebook often encounter a confusing alphabet soup of file format names — EPUB, MOBI, KFX, AZW, AZW3, KPF — and aren’t sure which they need, which KDP accepts, and which will produce the best result for readers. The short answer is: submit EPUB and let KDP handle the conversion. The longer answer involves understanding what each format actually is, because it affects your formatting workflow, your choice of tools, and your understanding of what readers actually receive on their devices.

The Kindle Format Ecosystem

Amazon has used several proprietary formats over the course of Kindle’s history. The current delivery format — what actually lands on a reader’s Kindle device or reading app — is KFX (Kindle Format X), Amazon’s most recent proprietary format. KFX supports enhanced typographic features including improved hyphenation, ligatures, and drop caps that older formats handled poorly.

Before KFX, Amazon used AZW3 (also called KF8) as its primary format, which itself replaced the older MOBI format. Authors who published in the early days of Kindle may remember submitting MOBI files to KDP. Amazon retired direct MOBI uploads in 2022 — KDP no longer accepts MOBI as an input format. If you encounter instructions telling you to submit a .mobi file, those instructions are outdated.

What KDP Currently Accepts for Upload

As of 2026, KDP accepts the following file formats for ebook upload: EPUB (.epub), Microsoft Word (.doc, .docx), HTML (.htm, .html), plain text (.txt), and RTF (.rtf). KDP converts all of these to its internal format for delivery to readers. The quality of that conversion varies significantly by input format.

EPUB is the overwhelmingly preferred input format and produces the most reliable, highest-quality conversion to KFX. EPUB is the open international standard for ebook publishing, maintained by the W3C. A correctly structured EPUB 3 file converts to KFX with minimal fidelity loss and produces consistent rendering across Kindle devices and reading apps. The EPUB 3 specification is maintained at w3.org/publishing/epub3/ for authors who want to understand the underlying standard.

Word documents (.docx) are accepted and convenient if Word is your writing tool, but KDP’s Word-to-KFX conversion is less predictable than EPUB-to-KFX. Common issues include inconsistent paragraph spacing, lost scene breaks, heading styles rendering differently across devices, and image positioning behaving unexpectedly. For a simple text-only book with minimal formatting, a Word submission is often adequate. For books with structured layouts, images, or specific typographic requirements, EPUB is strongly preferable.

EPUB 2 vs EPUB 3

EPUB has two active versions: EPUB 2 (the older standard, still widely supported) and EPUB 3 (the current standard with richer features). KDP accepts both. For most books, EPUB 3 is the better choice — it supports enhanced typographic features that KFX can leverage, including better hyphenation control and improved drop-cap handling. Modern formatting tools (Vellum, Atticus, Sigil) produce EPUB 3 by default. EPUB 2 remains perfectly acceptable for older workflows — the practical difference for most text-only fiction and non-fiction is minimal.

What Readers Actually Receive

When a reader purchases your Kindle ebook, Amazon delivers a KFX file to their device or app — not your original EPUB. KFX is Amazon’s proprietary delivery format and is not compatible with non-Amazon ebook readers like Kobo or Apple Books. This distinction matters if you’re also distributing wide: your wide distribution files should be your source EPUB, not anything Amazon has generated. See the Going Wide vs KDP Select guide for how distribution strategy affects your file workflow, and the ebook formatting guide for how to build a distribution-quality EPUB from scratch.

Readers using the Kindle Cloud Reader (in a browser), the Kindle iOS or Android app, or a physical Kindle device may all render your ebook slightly differently because different rendering engines are in use. The Kindle Paperwhite and Kindle Scribe use Amazon’s proprietary e-ink rendering engine; the mobile apps use a different rendering stack. Testing in KDP’s Online Previewer across simulated devices before publishing helps identify rendering differences before readers encounter them.

Enhanced Ebooks and Fixed-Layout Formats

Most Kindle ebooks are reflowable — the text adapts to the reader’s screen and font settings. But KDP also supports fixed-layout ebooks, where the layout is fixed exactly as designed and does not reflow. Fixed-layout is appropriate for children’s picture books (where the relationship between text and illustration must be preserved exactly), graphic novels, highly illustrated non-fiction, and cookbooks where layout is integral to usability.

Fixed-layout ebooks require a different EPUB structure and significantly more production complexity than reflowable ebooks. Each page is essentially a precise design canvas. Most self-published authors who need fixed-layout for children’s picture books either use a specialised tool (Book Creator, Adobe InDesign with a fixed-layout EPUB export workflow) or hire a professional formatter with fixed-layout experience, since the technical demands exceed what general-purpose formatting tools handle well. KDP’s fixed-layout requirements are documented in their Kids’ Book Creator and Enhanced Typesetting documentation.

File Size and Delivery Fees

Your submitted EPUB file size determines the delivery fee that KDP deducts from your 70% royalty for each sale. The delivery fee is $0.15 per megabyte of the converted file size — not the size of your original EPUB upload, but the size of the file KDP generates for delivery. Text-only ebooks typically convert to very small delivery files (0.3–0.8 MB), making delivery fees negligible. Image-heavy books — illustrated non-fiction, children’s books, books with many photographs — can have delivery files of 3–8 MB, which meaningfully reduces your per-sale royalty at the 70% rate. See the Kindle Ebook Pricing guide for worked examples of how delivery fees affect your actual earnings at different price points.

Optimising image files before including them in your EPUB — compressing JPEGs to 70–80% quality, sizing images to the maximum dimension they’ll be displayed at rather than larger — is the most direct way to keep your ebook delivery file size reasonable. Formatting tools like Atticus handle image compression automatically during export. If formatting manually, run your images through a compression tool like Squoosh or TinyPNG before embedding them.

Uploading and Converting Your File

Upload your EPUB (or other source file) through the KDP book setup interface under “Manuscript” in the content step. KDP converts the file and makes the converted result available for preview within a few minutes. Use KDP’s Online Previewer immediately after upload to check the conversion result before proceeding — don’t assume your submission looks correct based on how your source EPUB looked in your local EPUB reader, since KDP’s conversion can behave differently from other EPUB rendering environments.

If the conversion result contains errors or unexpected formatting, the cause is almost always in the source file rather than in KDP’s conversion process. Common root causes include: inconsistent paragraph styles in the source document, manual formatting overriding style definitions, incorrect heading structure preventing the NCX/Nav table of contents from generating, and image files in formats or sizes that don’t convert cleanly. Fixing these in the source EPUB and re-uploading is the correct resolution — don’t attempt to edit the converted KFX file directly.

The quality of your formatted ebook output is fundamentally limited by the quality of your source manuscript. Formatting cannot correct prose errors, structural inconsistencies, or unclear writing — and a clean, well-structured EPUB built from a proofread manuscript produces far fewer conversion surprises than one built from an unreviewed draft. Vappingo’s manuscript proofreading service gives you the clean, finalised text that makes the formatting and upload process reliable and straightforward.

KDP’s Kindle Create Tool

Amazon offers a free formatting tool called Kindle Create, available as a downloadable desktop application. Kindle Create imports Word documents and provides a visual formatting environment where you can apply chapter heading styles, select from themed book templates, and preview the result on simulated Kindle devices before exporting a KPF (Kindle Package Format) file for KDP upload. KPF is a format specific to Kindle Create — KDP accepts it directly without the need to generate an intermediate EPUB.

Kindle Create is a legitimate option for authors who want a free, guided formatting experience without the complexity of building an EPUB manually or the cost of a paid formatting tool. Its limitations are: the available design themes are relatively limited and produce books that look similar to each other, it has less typographic control than dedicated tools like Vellum or Atticus, and it doesn’t export a format suitable for wide distribution (the KPF file only works with KDP). Authors who plan to go wide to Apple Books, Kobo, and other platforms need a separate EPUB workflow regardless, making Kindle Create’s KPF output less useful than a standard EPUB would be. See the Going Wide vs KDP Select guide for how your distribution choice affects your formatting tool selection.

Enhanced Ebooks and Multimedia Formats

KDP supports two types of enhanced ebook beyond standard text: Enhanced Typesetting (a set of typographic improvements applied automatically by Kindle’s rendering engine to eligible titles) and Amazon’s older Enhanced Ebook format that supported audio and video embeds. Enhanced Typesetting — which enables features like improved hyphenation, kerning, drop caps, and chapter art rendering — is applied automatically to eligible EPUB 3 files and requires no special action from the author. You don’t need to configure or enable it; producing a correctly structured EPUB 3 makes your book eligible.

The multimedia Enhanced Ebook format (with embedded audio and video) is a separate product type with its own production requirements and is rarely used by self-published authors due to its complexity and the limited reader base on devices that support it. Most authors have no need for it. If you’re interested in the enhanced ebook possibility for a specialised non-fiction title, Amazon’s Kids’ Book Creator and Enhanced Ebook documentation cover the requirements — but the production investment is substantial and the market is niche. For the vast majority of self-published fiction and non-fiction, a well-formatted standard EPUB 3 is the right deliverable and the one that produces the best reading experience across the widest range of devices. The KDP Select and Kindle Unlimited guide covers how your ebook’s format and KU enrolment interact, which affects how KENP pages are counted from your formatted ebook.

Updating Your Ebook File After Publication

One significant advantage ebooks have over print books is that you can update them after publication. If you discover a formatting error, a broken link, or content that needs correction after your book is live, you can upload a corrected EPUB through KDP’s manuscript update process. KDP reviews the updated file and replaces the published version once approved — typically within 24–72 hours. Readers who have already purchased the book may receive the update automatically or may need to request it through their Kindle device settings, depending on the nature of the change.

Amazon has policies about significant content changes to published ebooks (changes that materially alter what buyers purchased may trigger a review process), but formatting corrections and minor text fixes are generally processed without issue. The ability to update is one reason why self-publishing can actually produce a more refined reader experience than traditional publishing over the book’s lifetime — errors discovered in post-publication reviews can be corrected for all future readers in a way that print books don’t allow. A good proofreading process before publication minimises the need for post-publication corrections, but it’s reassuring to know the option exists. Reedsy’s production guide at blog.reedsy.com covers the full self-publishing production workflow including post-publication updates in helpful detail.