What is a .mobi file? (MOBI)

MOBI is an older eBook format that Amazon adopted for early Kindles. It holds reflowable text like EPUB but is now largely retired in favour of EPUB and Amazon's newer formats.

What is a .mobi file used for?

MOBI was one of the first widely used eBook formats and became the basis for Amazon's early Kindle books.

Amazon has since moved on to AZW3 and KFX, and now accepts EPUB directly, so MOBI is mostly a legacy format you meet in older libraries.

Calibre reads MOBI and converts it to and from EPUB with ease.

How to open a .mobi file

The .mobi format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list. For a step-by-step walkthrough, see how to open a .mobi file.

Windows

Calibre
Kindle app

macOS

Calibre
Kindle app

Linux

Calibre
Foliate

Web

Not common; convert first

How to convert a .mobi file

You can convert a .mobi file to EPUB, PDF, AZW3 using a conversion tool or the export menu of an app that opens it.

.mobi file signature (magic bytes)

Programs recognise a .mobi file by the bytes at the start of the file, not by its name. These are the signatures for MOBI. For a full breakdown, see the MOBI file signature page.

Hex signature	Offset	Note
42 4F 4F 4B 4D 4F 42 49	60	'BOOKMOBI' at offset 60

See the full magic-numbers reference for every format.

Frequently asked questions