The Kindle file format is Amazon's proprietary way of storing e-books so they display correctly on Kindle devices and apps
When you buy a book from Amazon's Kindle store, you get a file in one of Amazon's own formats — most commonly .azw, .azw3, or .mobi. These are not the same as the .epub format that most other e-readers use. Amazon created its own formats to control how books look on Kindle devices and to prevent you from easily moving those books to a different brand of reader.
The practical result: a Kindle file will open on any Kindle device or the Kindle app (on your phone, tablet, or computer), but it will not open on a Kobo, Apple Books, or most other e-readers without conversion. If you buy from Amazon, you are locked into reading through Amazon's ecosystem. If you want to read the same book on multiple devices from different manufacturers, you need either a different file format or multiple copies of the book.
Key Takeaways
- Kindle files (.azw, .azw3, .mobi) are Amazon's proprietary formats and only work on Kindle devices and Amazon's Kindle app.
- Most other e-readers use the .epub format instead, which Kindle devices do not natively support.
- You can convert Kindle files to other formats using free tools like Calibre, though this removes DRM protection that Amazon adds to purchased books.
- If you want to read the same book across different devices and brands, buying DRM-free .epub files from independent publishers or libraries is simpler than converting.
- Amazon's Kindle app is free and works on phones, tablets, and computers, so you can read Kindle files on almost any device even if you do not own a Kindle reader.
The three main Kindle file formats and what they mean
.mobi was Amazon's original e-book format, used on older Kindle devices. It is still supported but largely phased out. If you see a .mobi file, it will work on Kindle devices, but Amazon now prefers the newer formats.
.azw is Amazon's standard format for Kindle books. It is essentially a wrapper around .mobi with added DRM (digital rights management) — the copy protection that prevents you from sharing the file. Most Kindle books you buy are in .azw format.
.azw3 is Amazon's newest format, designed for books with complex layouts, color images, or special formatting. Textbooks, graphic novels, and illustrated children's books often come in .azw3. It offers better quality than .azw but requires a newer Kindle device or app to read.
All three formats are proprietary to Amazon. None of them will open on a Kobo, Apple Books reader, or most other e-reading software without conversion.
Why Amazon uses its own file format instead of the standard .epub
The publishing industry standard is .epub, an open format that works across nearly all e-readers — Kobo, Apple Books, Google Play Books, most library apps, and many others. Amazon chose not to support .epub on Kindle devices, even though the company could easily do so.
The reason is control. By using its own formats, Amazon makes it harder for you to move your library to a competitor's device. If you have bought 200 books in Kindle format, switching to a Kobo reader means either leaving those books behind or spending time converting them. That friction keeps customers locked in. Amazon also uses DRM to prevent sharing and resale, which .epub files can also carry but which Amazon implements more restrictively.
From a practical standpoint, this means Kindle books are less portable than books in other formats. You can read them on any device that runs the Kindle app, but you cannot read them on a Kobo e-reader or most other hardware without conversion.
How to read Kindle files on devices other than Kindle hardware
The easiest path is to use Amazon's free Kindle app, available for iPhone, iPad, Android phones, Android tablets, Mac, and Windows. read the app, sign in with your Amazon account, and your Kindle library appears automatically. You do not need to own a Kindle device at all — the app lets you read any book you have purchased from Amazon.
If you want to read a Kindle file on a non-Amazon e-reader (like a Kobo), you need to convert the file. The free tool Calibre can convert .azw and .azw3 files to .epub or other formats. However, Calibre cannot remove the DRM protection on books you have purchased from Amazon — it can only convert DRM-free files. If you own a book you bought from Amazon and want to read it on a different device, you have two options: use the Kindle app on that device instead, or buy the book again from a publisher or store that sells DRM-free .epub files.
For books you have written yourself or obtained without DRM, Calibre works perfectly and takes about one minute per file.
When you might encounter Kindle files outside of Amazon
Most Kindle files come from Amazon's store, but not all. Self-published authors sometimes distribute .mobi or .azw files directly to readers. Project Gutenberg and other sites that distribute public domain books often offer Kindle formats alongside .epub and other options. If someone sends you a Kindle file by email or you read one from a website, it will still only open on Kindle devices or the Kindle app — the format does not change based on where it came from.
Some publishers also sell .azw files directly, though this is less common than selling through Amazon. In those cases, the file usually still has DRM, so the same restrictions explore.
Comparing Kindle files to other e-book formats you might use
| Format | Works on | DRM common? | Best for |
|---|---|---|---|
| .azw / .azw3 | Kindle devices and Kindle app only | Yes (on purchased books) | Books bought from Amazon |
| .epub | Kobo, Apple Books, most libraries, many others | Sometimes | Books from independent publishers, libraries, DRM-free stores |
| Any device with a PDF reader | Sometimes | Textbooks, documents, books with fixed layouts | |
| .mobi | Older Kindle devices, some e-readers | Varies | Older Kindle files (rarely used now) |
How to avoid being locked into one format
If you want flexibility to read books on multiple devices and brands, buy from stores that sell .epub files or DRM-free books. Project Gutenberg, Standard Ebooks, Smashwords, and many independent publishers sell .epub files you can read on any device. Some libraries lend .epub files through apps like Libby or OverDrive, which work on most e-readers.
You can also buy from Amazon and use the Kindle app on your other devices — this works well if you own a phone or tablet but not a dedicated Kindle reader. The Kindle app is free and syncs your reading progress across devices, so you can start a book on your phone and continue on your computer.
The trade-off is convenience versus choice. Amazon's ecosystem is seamless if you stay within it, but it costs you portability. Other formats give you more freedom but require more setup.
Frequently Asked Questions
Can I read a Kindle file on my Kobo e-reader?
Not directly. Kobo uses .epub format, and Kindle devices use .azw or .azw3. You would need to convert the Kindle file to .epub using a tool like Calibre, but this only works if the file does not have DRM protection. Books you purchased from Amazon have DRM and cannot be converted without removing the protection, which is legally complex. The simpler option is to use the free Kindle app on a phone or tablet instead.
What is the difference between .azw and .azw3?
.azw is the standard Kindle format for most books. .azw3 is newer and handles complex layouts, color images, and special formatting better — it is commonly used for textbooks, graphic novels, and illustrated books. Both work on modern Kindle devices and the Kindle app, but .azw3 requires newer hardware or software versions. For plain text novels, the difference is invisible.
If I buy a Kindle book, can I lend it to someone else?
Amazon allows lending on some books for 14 days, but not all publishers permit it. You cannot straightforward send the file to someone else — lending happens through Amazon's system, and the recipient needs an Amazon account and Kindle app or device. The book is not available to you while someone else is borrowing it.
Do I need to own a Kindle device to read Kindle books?
No. The free Kindle app works on phones, tablets, and computers. You can read any book in your Kindle library on any of these devices by signing in with your Amazon account. Many people read Kindle books exclusively on their phones or tablets and never buy a dedicated Kindle reader.
Can I convert a Kindle file to PDF?
Calibre can convert .azw and .azw3 files to PDF, but again, only if the file has no DRM protection. Books purchased from Amazon have DRM, so conversion is not straightforward. For DRM-free Kindle files (usually from self-published authors or Project Gutenberg), conversion to PDF works fine and takes about a minute.