Kindle reads its own format, plus PDFs and a few others
Amazon's Kindle devices read AZW3 (the current standard), AZW (older Kindle books), PDF, and MOBI files natively. If you own an e-book in EPUB format — the most common format for library loans and independent publishers — your Kindle cannot read it directly. You will need to convert it first, or use a different device.
The file type matters because it determines whether you can move a book between devices, lend it, or read it years from now. Amazon's formats lock books to Amazon's ecosystem. Open formats like EPUB and PDF work on almost any device. Understanding the difference helps you avoid buying the same book twice or losing access to something you paid for.
Key Takeaways
- Kindle devices read AZW3, AZW, PDF, and MOBI files, but not EPUB — the standard format for library e-books.
- Books you buy from Amazon arrive in AZW3 format and can only be read on Kindle devices or Amazon's free reading apps.
- PDFs work on Kindle but may not reflow text to fit the screen, making them harder to read on smaller devices.
- Library e-books in EPUB format require conversion software (like Calibre) before a Kindle can open them.
- If you want to read the same e-book across multiple devices without conversion, EPUB is the better choice than Kindle's proprietary formats.
AZW3 and AZW: Amazon's proprietary formats
AZW3 is what Amazon uses for most Kindle books sold today. It is a compressed format that lets text reflow to fit different screen sizes — so the same book reads properly on a Kindle Paperwhite, a Kindle Scribe, or the Kindle app on your phone. Amazon also uses AZW3 for books with images, comics, and fixed layouts.
AZW is the older format Amazon used before 2011. Older Kindle devices still read it, and some publishers still distribute in AZW, but you will rarely encounter it unless you own a very old Kindle or buy from a specialized publisher. If you see AZW files in your library, they will work on any Kindle device, but they cannot be read on non-Amazon devices.
Both formats are proprietary to Amazon. Books in AZW or AZW3 carry digital rights management (DRM) encryption, which means you cannot legally copy them to another device or share them, even with family members on the same account. You can read them only through Amazon's ecosystem — Kindle devices or Amazon's free reading apps.
PDF: Works but has limitations on Kindle
Kindle devices can open PDF files directly. This is useful if you have a research paper, a manual, or a self-published book in PDF format. You can email a PDF to your Kindle's email address (found in your Amazon account settings), and it will appear in your library within minutes.
The catch: PDFs do not reflow. If the PDF was designed for a standard 8.5-by-11-inch page, the text will be tiny on a Kindle's smaller screen. You can zoom in, but then you have to scroll left and right to read each line. For documents with lots of text, this becomes tedious. PDFs work better on larger Kindle devices like the Kindle Scribe (10.2 inches) than on the basic Kindle (6 inches).
PDFs are also not encrypted by Amazon, so you can copy them to other devices freely. If you have a choice between a PDF and an AZW3 version of the same book, the PDF gives you more flexibility — you can read it on a tablet, a computer, or a phone without needing Amazon's apps.
MOBI: An older open format that Kindle still reads
MOBI was an open e-book format created before EPUB became the standard. Kindle devices read MOBI files, and you can find them from some independent publishers and older e-book sources. MOBI files reflow text like AZW3 does, so they read well on Kindle screens.
MOBI is becoming less common. Most publishers and libraries have switched to EPUB. If you find a MOBI file, it will work on your Kindle, but you may not be able to read it anywhere else. For new purchases or library loans, you are more likely to encounter EPUB.
EPUB: The standard format that Kindle cannot read
EPUB is the open standard for e-books. Libraries lend books in EPUB. Independent publishers use EPUB. Most non-Amazon e-readers (Kobo, Apple Books, Google Play Books) read EPUB natively. If you want to own an e-book that works on multiple devices without vendor lock-in, EPUB is the format to look for.
Kindle does not read EPUB. If you borrow an EPUB book from your library and want to read it on a Kindle device, you have two options: convert it to AZW3 using free software like Calibre, or use the Kindle app on your phone or tablet instead (which does not require conversion). Converting removes the library's DRM protection, which is legal for personal use in most jurisdictions, but the process takes a few extra steps.
EPUB files are not locked to one device or ecosystem. You can read the same EPUB book on your phone, your tablet, your computer, and a Kobo e-reader without buying it multiple times. This flexibility is why libraries and independent publishers prefer EPUB.
How to convert EPUB to Kindle format
If you have an EPUB file and want to read it on a Kindle device, read and install Calibre (free, available for Windows, Mac, and Linux). Open Calibre, click "Add books," select your EPUB file, then click "Convert books." Choose AZW3 as the output format, and Calibre will create a new file you can email to your Kindle or transfer via USB.
This process removes DRM from library books, which is legal for personal use but violates the terms of service with some publishers. If the EPUB file has no DRM (common with independent publishers and older library systems), conversion is straightforward and carries no legal risk.
Alternatively, you can read EPUB files on the Kindle app for your phone or tablet without converting. The Kindle app does not read EPUB natively, but you can use a separate app like Libby (for library books) or Apple Books, Google Play Books, or Kobo to read EPUB files on the same device. This avoids conversion entirely.
Comparing file types for different reading situations
| File Type | Kindle Device | Other Devices | Best For |
|---|---|---|---|
| AZW3 | Yes, native | Only Amazon apps | Books purchased from Amazon; locked to Kindle ecosystem |
| AZW | Yes, native | Only Amazon apps | Older Kindle books; rarely used today |
| MOBI | Yes, native | Some older devices | Independent publishers; becoming obsolete |
| Yes, but text does not reflow | Any device with PDF reader | Documents, manuals, research papers | |
| EPUB | No, requires conversion | Most e-readers, phones, tablets | Library loans, independent publishers, device flexibility |
Frequently Asked Questions
Can I read a library book on my Kindle?
Only if your library lends in MOBI or PDF format, which is rare. Most libraries lend in EPUB. You can convert the EPUB to AZW3 using Calibre, or read it on the Kindle app for your phone or tablet instead. Check your library's website to see what formats they offer.
What happens if I email a PDF to my Kindle?
It arrives in your Kindle library within minutes and you can open it on any of your Kindle devices. The text will not reflow, so it may be small or require scrolling on smaller screens. PDFs work best on the Kindle Scribe or other large-screen Kindles.
If I buy a Kindle book, can I read it on my iPad?
Yes, if you read the free Kindle app from the App Store. Books you buy from Amazon in AZW3 format can be read on the Kindle app for iPad, iPhone, Mac, or Android. You cannot read them in other e-reader apps like Apple Books or Kobo.
Is converting EPUB to AZW3 legal?
Converting for personal use is legal in most countries, including the United States. If the EPUB file has DRM (digital rights management), removing it to convert may violate the Digital Millennium Copyright Act, though enforcement against personal use is rare. Library books often have DRM; books from independent publishers usually do not.
Why does Amazon use its own format instead of EPUB?
Amazon's proprietary formats lock customers into the Kindle ecosystem, which benefits Amazon's business. EPUB is an open standard that works across devices and publishers, which is better for readers but gives Amazon less control. This is why Kindle books are often cheaper than the same book in EPUB — Amazon subsidizes the price to encourage lock-in.