Kindle uses its own format called AZW, which Amazon created to lock books to their ecosystem

Amazon's Kindle devices and apps read AZW files — a proprietary format Amazon developed based on the older Mobipocket standard. When you buy a book from the Kindle Store, you receive an AZW file (or AZW3 for newer titles with better formatting). This format includes digital rights management, or DRM, which means the file is encrypted and tied to your Amazon account. You cannot read an AZW file on a Kobo reader, a Nook, or most other e-readers without converting it first.

Amazon also accepts several other formats directly on Kindle devices and apps: PDF, TXT, MOBI, and HTML. If you have a book in one of these formats from another source, you can sideload it onto a Kindle device by connecting it to your computer via USB, or email it to your Kindle email address (a unique address Amazon assigns to each device). The Kindle will convert these formats automatically so they display properly on your screen.

The practical consequence is this: if you want to read the same book across multiple devices — a Kindle tablet, a Kobo e-reader, and your phone — you need the book in a format that works on all three. That usually means EPUB, which is the open standard most non-Amazon devices support.

Key Takeaways

  • Kindle books from the Amazon store come in AZW format and are locked to your Amazon account, so you cannot read them on other brands of e-readers.
  • You can sideload PDF, TXT, MOBI, and HTML files onto a Kindle device by connecting it to a computer or emailing the file to your device's Kindle email address.
  • EPUB is the standard format for most other e-readers and reading apps, so a book in EPUB format will work on Kobo, Nook, Apple Books, and most library apps.
  • If you own a book in AZW format and want to read it elsewhere, you will need to convert it using a tool like Calibre, though this removes the DRM protection.

Why Amazon uses its own format instead of the industry standard

EPUB is the open standard that most of the publishing industry uses. It works on Kobo devices, Nook readers, Apple Books, Google Play Books, and the vast majority of library apps. Amazon deliberately chose not to support EPUB on Kindle devices, even though it would be technically straightforward to do so. The reason is control: by using AZW, Amazon ensures that readers who buy Kindle books stay within the Kindle ecosystem.

This matters to you because it affects your choices. If you buy heavily from the Kindle Store, you are locked into reading on Amazon devices and apps. If you want flexibility — the ability to read the same book on multiple devices or to switch platforms later — you need to buy books in EPUB format from other retailers, borrow from libraries that lend EPUB files, or convert your books yourself.

How to convert AZW to EPUB or other formats

If you own an AZW file and want to read it on a non-Kindle device, you can convert it using Calibre, a free, open-source tool that runs on Windows, Mac, and Linux. read Calibre from calibre-ebook.com, install it, and open the program. Click "Add books" and select your AZW file. Right-click the book in your library and select "Convert books." Choose EPUB as the output format and click "OK." Calibre will create an EPUB version in your library.

This process removes the DRM protection from the file, which is legal in most jurisdictions for personal use but violates Amazon's terms of service. Amazon does not actively pursue individual users who convert their own books, but you should know the legal status before you proceed.

Other conversion tools exist — some online, some desktop — but Calibre is the most reliable and widely used. It also handles batch conversions, so if you have many books to convert, you can do them all at once instead of one by one.

What format to use if you want to read across multiple devices

If you are building a library that you want to access on Kindle, a tablet, a phone, and possibly a dedicated e-reader, EPUB is your safest choice. Most libraries lend books in EPUB format through apps like Libby or OverDrive. Many independent publishers and retailers sell EPUB files directly. Project Gutenberg, a free library of public-domain books, offers EPUB downloads for thousands of titles.

You can read EPUB files on a Kindle device or app by converting them to AZW using Calibre (the reverse of the process above), but this adds an extra step. If you are starting from scratch and want maximum flexibility, consider buying from retailers that sell EPUB directly, borrowing from your library, or using reading apps like Apple Books or Google Play Books that work across devices without format conversion.

The trade-off is convenience versus control. The Kindle Store is large, well-organized, and integrated with Kindle devices. But that integration comes at the cost of being locked into Amazon's ecosystem. Other retailers and libraries offer less convenience but more freedom to read where you want.

Sideloading books onto your Kindle device

Sideloading means transferring a file directly to your device instead of downloading it through the Kindle Store. To sideload a PDF, TXT, MOBI, or HTML file, connect your Kindle device to your computer with a USB cable. Your computer will recognize the Kindle as a removable drive. Open the drive, locate the "documents" folder, and drag your file into it. Disconnect the device, and the file will appear in your Kindle library within a few seconds.

Alternatively, you can email the file to your device's Kindle email address. Every Kindle device has a unique email address that looks like "yourname@kindle.com." Find this address in your device settings or in your Amazon account under "Manage Your Content and Devices." Send the file as an attachment to that address, and it will appear on your device within minutes. This method works from any computer or phone, so it is useful if you do not have USB access.

Sideloading is useful for books you own in other formats, documents you want to read on your Kindle, or books from sources outside the Kindle Store. The Kindle will convert the file automatically, though formatting may not be perfect — PDFs in particular sometimes display oddly on small screens.

The difference between AZW, AZW3, and MOBI

MOBI is the older format that Kindle used before Amazon developed AZW. Many older Kindle books and self-published titles still use MOBI. Kindle devices and apps still read MOBI files, and you can sideload them onto your device. However, MOBI is gradually being phased out in favor of AZW3.

AZW is Amazon's proprietary format, used for most Kindle books purchased from the store. It is based on MOBI but includes DRM encryption and better support for newer features like embedded fonts and advanced formatting.

AZW3 is the newest Kindle format, used for most new releases and books with complex layouts. It supports better typography, color, and interactive elements. If you buy a recent book from the Kindle Store, it will almost certainly be AZW3. All three formats work on Kindle devices and apps, so you do not need to worry about which one you have — the device handles the difference automatically.

Frequently Asked Questions

Can I read a Kindle book on my phone if I do not have the Kindle app?

No. AZW files are encrypted and tied to your Amazon account, so you need either the official Kindle app or a Kindle device to read them. The Kindle app is free and available on iPhone, Android, iPad, and most tablets. If you want to read on your phone without the Kindle app, you would need to convert the AZW file to EPUB or another open format first.

What happens if I convert a Kindle book to EPUB and share it with someone else?

Sharing a converted file is copyright infringement, the same as sharing a physical book you do not own. Converting a book you own for your own use is generally legal, but distributing it to others is not. The DRM on the original AZW file exists partly to prevent this kind of sharing.

Do library books borrowed through Libby or OverDrive work on Kindle?

Most library apps lend books in EPUB format, which Kindle devices do not natively read. You can convert the EPUB to AZW using Calibre and then sideload it onto your Kindle, but this adds an extra step. It is usually simpler to read library books in the library's app or on a device that supports EPUB directly.

Is there a way to remove DRM from Kindle books without using Calibre?

Calibre is the most straightforward method. Some other tools exist, but they are less reliable and may violate terms of service or local laws. Calibre is free, widely supported, and works consistently across devices and operating systems.

If I buy a book in MOBI format, can I read it on my Kindle?

Yes. Kindle devices and apps read MOBI files natively. You can sideload a MOBI file onto your device the same way you would sideload a PDF — either by connecting via USB or by emailing it to your Kindle email address. The device will display it without any conversion needed.