EPUB is the standard file format for e-books on most devices
EPUB stands for Electronic Publication. It is the format that most e-readers — like Kobo, Apple Books, and many others — use to display books. When you download a book to read on your phone, tablet, or dedicated e-reader, there is a good chance it is an EPUB file, even if you do not see the file extension.
EPUB works differently from a PDF or a printed book. Instead of locking the text to a fixed page size, EPUB lets the text reflow. That means you can change the font size, the font itself, the line spacing, and the margins, and the book adjusts automatically. The same file works on a phone screen, a tablet, and a large e-reader without needing three different versions.
Amazon's Kindle uses its own format called MOBI (or AZW), so Kindle books are the main exception. But outside of Kindle, EPUB is what you will encounter almost everywhere.
Key Takeaways
- EPUB is a reflowable format, meaning text adjusts to fit your screen size and your chosen font settings instead of staying locked to a fixed page.
- Most e-readers and reading apps support EPUB, with Kindle being the major exception — Kindle uses MOBI or AZW format instead.
- EPUB files are smaller than PDFs and use less battery on e-readers because they contain only text and basic formatting, not images of entire pages.
- You can read EPUB files on almost any device using free reading apps, even if your device is not a dedicated e-reader.
How EPUB files work differently from PDFs
A PDF is a snapshot. It shows you exactly what a page looks like — the same layout, the same margins, the same font size — no matter what device opens it. That is useful for documents that need to look identical everywhere, like tax forms or instruction manuals. But for a novel or a textbook, it means you are stuck with whatever font size the creator chose.
EPUB does the opposite. It stores the text and tells your device what the text is — a heading, a paragraph, italics, a chapter break — but not exactly where to put it on screen. Your device reads those instructions and arranges the text based on your settings. Make the font bigger, and the text reflows to fit. Switch from portrait to landscape, and it reflows again. This is why EPUB is called a reflowable format.
This also makes EPUB files much smaller. A PDF of a 300-page novel might be 5 or 10 megabytes because it contains an image of every page. The same novel in EPUB might be 500 kilobytes because it contains only the text and the formatting instructions. Smaller files mean faster downloads and less drain on your e-reader battery.
What devices and apps can open EPUB files
Almost every e-reader except Kindle can open EPUB natively. Kobo, Nook, Tolino, and most other dedicated e-readers all use EPUB. If you own one of these devices, you can load EPUB files directly onto it, usually by connecting it to a computer and dragging the file into the right folder.
On phones and tablets, you have many choices. Apple Books (on iPhone and iPad) reads EPUB. Google Play Books reads EPUB. Libby, the free library app, delivers EPUB files. Calibre, a free desktop program, can open and convert EPUB files. On Android, apps like Moon+ Reader and Lithium also support EPUB. On Windows and Mac, you can read EPUB in a web browser using free online readers.
The one major device that does not support EPUB is the Amazon Kindle. Kindle uses MOBI or AZW format instead. If you want to read a book on Kindle, you need the book in Kindle format, or you need to convert it first using a tool like Calibre.
Where EPUB files come from
Most EPUB files come from publishers and retailers. When you buy an e-book from a store like Smashwords, Draft2Digital, or many independent bookstores, you can often download it in EPUB format. Libraries that lend e-books through apps like Libby and OverDrive deliver EPUB files. Project Gutenberg, which offers free public-domain books, provides EPUB versions of thousands of titles.
You can also create your own EPUB files. If you have a Word document, a Google Doc, or even a plain text file, you can convert it to EPUB using free tools like Calibre or online converters. This is useful if you want to read your own writing on an e-reader, or if you want to format a document for sharing with others.
Some websites and publishers protect EPUB files with digital rights management, or DRM. DRM is encryption that prevents you from copying or sharing the file. If an EPUB has DRM, you can still read it on any device that supports EPUB, but you cannot remove the protection or give the file to someone else. Many independent publishers and libraries do not use DRM, so you can move those files freely between your devices.
EPUB versions and what changed between them
EPUB has gone through several versions. EPUB 2 was the standard for many years and is still in use. EPUB 3, released in 2011, added support for audio, video, and better styling options. Most devices and apps today support both EPUB 2 and EPUB 3, so you do not usually need to worry about which version you have.
The differences matter mainly to publishers and developers. For a reader, the main thing to know is that newer devices and apps handle EPUB 3 better, especially if a book includes audio or video content. But a basic novel in EPUB 2 will open and read the same way on almost any device made in the last ten years.
How to convert other formats to EPUB
If you have a book in a different format — a PDF, a Word document, or even a plain text file — you can convert it to EPUB using Calibre, which is free and works on Windows, Mac, and Linux. Download Calibre, open it, click "Add books," select your file, then click "Convert books." Choose EPUB as the output format and click "OK." Calibre will create an EPUB version in your library.
Online converters like CloudConvert and Zamzar also work, though they usually have file size limits. Upload your file, choose EPUB as the output format, and download the result. These are useful if you do not want to install software, but they send your file to a server, so use them only for files you do not mind sharing.
Keep in mind that conversion quality depends on the source format. A Word document with simple formatting converts cleanly. A complex PDF with images and multiple columns may not convert perfectly, and you may need to fix the formatting by hand afterward.
Frequently Asked Questions
Can I read EPUB files on my Kindle?
Not directly. Kindle uses MOBI or AZW format, not EPUB. You can convert an EPUB to MOBI using Calibre, then send it to your Kindle. Alternatively, you can read EPUB files on your phone or tablet using a reading app, even if you own a Kindle.
Is EPUB the same as PDF?
No. EPUB is reflowable — the text adjusts to your screen and your settings. PDF is fixed — it shows the same layout on every device. EPUB files are usually much smaller and work better on phones and e-readers. PDFs are better for documents that need to look identical everywhere.
Do I need special software to open an EPUB file?
No. If you have an e-reader, it probably opens EPUB natively. On a phone or tablet, you can use a free reading app like Apple Books, Google Play Books, or Libby. On a computer, you can use a free app like Calibre or read it in your web browser using a free online reader.
Can I edit an EPUB file?
Yes, but it requires more work than editing a Word document. EPUB files are actually folders containing HTML and CSS files. You can unzip an EPUB, edit the HTML in a text editor, and rezip it. Calibre also has an editor built in. For simple changes like fixing typos, this is manageable. For major formatting changes, it is easier to convert back to Word, edit there, and convert to EPUB again.
What is the difference between EPUB 2 and EPUB 3?
EPUB 3 supports audio, video, and more advanced styling. EPUB 2 is older and simpler. Most devices support both. For a basic novel with no media, the difference is invisible to you. For a book with audio or interactive elements, EPUB 3 is necessary.