Free online MOBI to FB2 converter

Some e-readers and reading applications support FB2 but not legacy MOBI files, so a Kindle or Mobipocket book may need conversion before it can be opened, edited, or shared. FB2 also provides a more inspectable XML structure for cataloging and long-term storage.

What the MOBI format is

MOBI is an ebook format developed from Mobipocket and used extensively by older Amazon Kindle software and devices. A MOBI book normally contains reflowable text, metadata, a table of contents, images, and basic styling; it is still common in older Kindle libraries and ebook archives.

The .mobi extension can identify different internal variants, including older MOBI content and files that contain Kindle Format 8 data. DRM-protected books generally cannot be converted by ordinary software. Use an unprotected copy supplied by the rights holder or an authorized service; do not attempt to bypass DRM.

What the FB2 format is

FB2, or FictionBook 2, is an XML-based ebook format designed mainly for novels and other structured prose. It represents paragraphs, sections, headings, poems, quotations, notes, author information, cover data, and images as document elements instead of depending primarily on page layout.

FB2 is supported by FBReader and many open-source reading applications. Its reflowable structure adapts to different screens, while its readable XML makes text and metadata relatively easy to inspect, edit, validate, and catalog. Support is not universal, so check that the destination reader accepts FB2 before converting a large library.

Convert online on 101convert.com

1. Open the MOBI-to-FB2 converter on 101convert.com; it can be used free without installing software.
2. Upload the .mobi file and choose FB2 as the output format.
3. Start the conversion and download the generated .fb2 file when processing finishes.
4. Open the result in an FB2 reader and check the title, author, chapter list, paragraphs, notes, cover, and illustrations.

Do not upload DRM-protected, confidential, or unpublished books unless the service’s handling of uploaded files is acceptable for that material.

Convert with Calibre

1. Install the current version of Calibre and select Add books to import the MOBI file.
2. Select the book and choose Convert books.
3. Set FB2 in the output-format selector in the upper-right corner.
4. Review the metadata, cover, structure, and conversion options. Adjust the table of contents or chapter-detection settings if necessary, then select OK.
5. Open the book’s Calibre library folder and locate the generated .fb2 file, or right-click the book and choose the option to open its containing folder.

Calibre also includes a command-line converter:

ebook-convert input.mobi output.fb2

Quote paths containing spaces, for example ebook-convert "My Book.mobi" "My Book.fb2". The command uses Calibre’s default settings; conversion options can be added when precise control over structure, metadata, or images is required.

Quality and compatibility limits

Conversion reconstructs the book’s content and structure; changing .mobi to .fb2 does not convert the file. Ordinary prose usually transfers well, but complex CSS, fixed-position elements, tables, sidebars, embedded fonts, interactive content, and unusual footnotes may be simplified or omitted because FB2 has a narrower layout model.

Inspect headings and chapters after conversion because MOBI navigation data does not always map correctly to FB2 sections. Check cover and illustration dimensions, placement, captions, quotations, notes, and special characters. If the output reader reports an XML error, regenerate the file with Calibre or another trusted converter; manual edits must preserve valid XML syntax, escaping, and character encoding.