Kindle uses .mobi, .azw, and .azw3 formats, depending on the device and when the file was created
.mobi was Kindle's original format for ebooks. Amazon still accepts it, but the company stopped using it as the default around 2014. If you find a .mobi file in the wild, it will open on any Kindle device or the Kindle reading app, though newer devices may convert it to .azw3 behind the scenes.
.azw is Amazon's proprietary format, introduced to add digital rights management (DRM) protection to .mobi files. For practical purposes, .azw and .mobi behave the same way — they open on Kindles and Kindle apps. You will see both in older ebook libraries.
.azw3 is the current standard. Amazon introduced it around 2011 and made it the default for new purchases and uploads. It supports better typography, embedded fonts, and responsive layouts. If you buy an ebook from Amazon today, you are getting .azw3.
If you are uploading your own documents to Kindle (through Amazon's "Send to Kindle" service or Kindle Direct Publishing), you do not need to convert them to these formats first. Amazon accepts Word documents (.docx), PDFs, plain text (.txt), HTML, and several others, then converts them automatically.
Key Takeaways
- Amazon's current ebook format is .azw3, used for all new Kindle purchases and the most recent devices.
- .mobi and .azw are older formats that still work on Kindles but are no longer the default.
- You do not need to convert documents to Kindle formats yourself — Amazon accepts Word, PDF, and plain text and handles the conversion.
- The format matters most if you are moving ebooks between devices or removing DRM protection, less so if you are reading through Amazon's ecosystem.
Why Amazon uses multiple formats
Amazon introduced different formats at different times as ebook technology changed. .mobi was simple and worked on early e-ink devices with limited processing power. .azw added copy protection without changing the underlying file structure much. .azw3 came later when devices could handle more complex layouts — it supports CSS styling, embedded fonts, and reflowable text that adjusts to screen size.
The company kept older formats working because millions of ebooks were already in .mobi and .azw. Dropping support would have broken existing libraries. Instead, Amazon's newer Kindle devices (Paperwhite, Oasis, and recent basic models) can read all three, though they may silently convert .mobi to .azw3 when you open it.
How to check what format your ebook is
On a Kindle device, open the book and press the Menu button (three horizontal lines). Select "Book Details" or "About This Book." The format will be listed there — usually as "Format: Kindle eBook" or "Format: PDF" depending on what you sent to the device.
On a computer, right-click the file and select "Properties" (Windows) or "Get Info" (Mac). The file extension will be visible in the filename — look for .mobi, .azw, .azw3, or .pdf. If the file has no extension, check the file type field in the properties window.
If you bought the book from Amazon, you can also check your library on Amazon.com. Go to "Manage Your Content and Devices," find the book, and click the three dots next to it. Select "Download & Transfer via USB" to see what formats are available for that title.
Converting between formats if you need to
If you have an ebook in .mobi or .azw and want to convert it to .azw3 (or vice versa), the most common tool is Calibre, a free, open-source ebook manager. Download it, add your book to the library, select it, click "Convert Books," choose your output format, and click "OK." Calibre handles most ebook formats and can also strip DRM from some files, though that depends on the book's protection level.
Online converters like CloudConvert and Zamzar also work, but they upload your file to their servers. If the ebook has DRM protection, these tools will not remove it — only Calibre with the right plugins can do that, and the legality varies by jurisdiction.
For most readers, conversion is unnecessary. Kindle devices and apps read .mobi, .azw, and .azw3 equally well. You only need to convert if you are moving ebooks to a non-Amazon device (like a Kobo or iPad) or if you are removing DRM to read on multiple platforms.
What happens when you send documents to Kindle
Amazon's "Send to Kindle" feature lets you email documents to your Kindle device or app. You can send Word documents, PDFs, images, and HTML files. Amazon converts them automatically — you do not choose the output format. The conversion usually produces a .azw3 file on newer devices, though older Kindles may receive .mobi instead.
The conversion process is not perfect. Complex PDFs with multiple columns, images, or unusual fonts may not reflow well on small screens. Word documents usually convert cleanly because they have simpler structure. If the conversion looks wrong, try converting the file to PDF first, then sending the PDF to Kindle — sometimes that produces better results.
DRM protection and format choice
All ebooks sold through Amazon come with DRM (Digital Rights Management) protection, regardless of format. This means you cannot copy the file to another device or share it. The format itself does not determine whether DRM is present — .azw3 files can be protected or unprotected, as can .mobi files.
If you publish your own ebook through Kindle Direct Publishing, you can choose whether to enable DRM. Disabling it means readers can move the file between devices more freely, but it also makes it easier to share illegally. Most indie authors leave DRM on for the same reason traditional publishers do.
Frequently Asked Questions
Can I read a .mobi file on a newer Kindle?
Yes. All current Kindle devices and apps read .mobi files. Amazon may convert them to .azw3 in the background, but you will not see that happen — the book will open and read normally. The only difference you might notice is that .mobi files sometimes display slightly differently than .azw3 files because of how the newer format handles fonts and spacing.
What format should I use if I am self-publishing on Kindle?
Upload your manuscript as a Word document (.docx) or PDF. Kindle Direct Publishing converts it automatically to .azw3. You do not need to do the conversion yourself. If you want to see what the final ebook will look like before publishing, use KDP's preview tool — it shows you exactly how your book will appear on different Kindle devices.
Why does my PDF look different on Kindle than on my computer?
Kindle devices have small screens and lower resolution than computers. PDFs designed for 8.5-by-11-inch pages shrink down, making text tiny. If you are sending a PDF to Kindle, try converting it to a reflowable format first (like .azw3 or .mobi) so text resizes to fit the screen. Calibre can do this conversion.
Can I remove DRM from a Kindle ebook?
Technically yes, but the legality depends on where you live. In the United States, the Digital Millennium Copyright Act (DMCA) makes it illegal to circumvent DRM even for personal use, though enforcement is rare. Other countries have different rules. Calibre has plugins that can remove DRM, but using them may violate your local laws.
Is .azw3 better than .mobi?
.azw3 supports better typography, embedded fonts, and more complex layouts, so it is technically superior. But for simple novels with plain text, the difference is invisible. .azw3 matters more for books with lots of images, special formatting, or multiple languages. If you are just reading a straightforward ebook, either format works fine.