Free online EPUB to MOBI converter

Older Kindle devices and applications may require a .mobi file instead of an EPUB, especially when a book must be sideloaded or opened by legacy software. Converting creates a separate MOBI copy while preserving the original EPUB for editing, publishing, or other reading systems.

What the EPUB format is

EPUB is an open ebook format built from HTML, CSS, metadata, and packaged resources such as images and fonts. Its reflowable layout adapts text to screen size, font settings, and orientation.

Publishers, ebook editors, libraries, and authors commonly use EPUB for Apple Books, Kobo, Google Play Books, and other platforms. EPUB files may be created or edited with Sigil, Adobe InDesign, Calibre, and word processors that support ebook export.

What the MOBI format is

MOBI is a legacy Mobipocket-based ebook format associated with older Amazon Kindle hardware and software. It stores reflowable text, basic metadata, a table of contents, and images in a compact package, but supports fewer CSS and layout features than EPUB.

MOBI remains useful when a particular older Kindle application, device, or local workflow accepts MOBI but not EPUB. Amazon no longer recommends MOBI for current Kindle publishing workflows; EPUB is the normal upload format, and Amazon converts it to newer delivery formats such as AZW3 or KFX. Newer Kindle devices can also receive EPUB through Send to Kindle, although direct USB support for EPUB is not universal.

How to convert an EPUB file to MOBI

Calibre is the most practical desktop option for individual and batch conversions.

1. Install and open Calibre, then choose Add books and select the .epub file.
2. Select the imported book and choose Convert books → Convert individually.
3. Set the output format in the conversion dialog to MOBI.
4. Check the title, author, cover, and table of contents. Use Look & feel only if margins, fonts, or source styling need adjustment.
5. Click OK. When conversion finishes, select the book and choose Open containing folder to find the generated .mobi file.

Calibre also provides the ebook-convert command-line utility:

ebook-convert input.epub output.mobi

Metadata can be supplied as options, for example:

ebook-convert input.epub output.mobi --title "Book title" --authors "Author Name"

If installing software is not suitable, 101convert.com can convert an EPUB to MOBI online for free: upload the EPUB, choose MOBI, start the conversion, and download the result. Do not upload DRM-protected, confidential, or unpublished files unless the service and your rights permit it.

Quality and compatibility limits

Inspect the result on the Kindle application or device that will open it. MOBI conversion can change complex CSS, fixed-layout pages, embedded fonts, SVG graphics, interactive content, footnotes, tables, image positioning, and right-to-left text.

Validate and repair the source EPUB before converting. Sigil or EPUBCheck can help identify malformed HTML, broken references, invalid metadata, and navigation problems; correcting the source usually produces better results than repeatedly changing conversion settings.

DRM-protected EPUB files generally cannot be converted by Calibre or a conversion service. Use an unprotected copy supplied by the publisher or a supported transfer method rather than attempting to bypass DRM.

Keep the original EPUB: conversion may discard CSS rules, semantic markup, fonts, accessibility metadata, or other features that MOBI cannot represent.