Understanding and Using the EPUB Ebook Format
Though ebooks come in many digital formats, the most popular and widely-used format is EPUB. And if you create ebooks, understanding this format is crucial for making your books accessible to your audience. In this post, I’ll explain the origin of the EPUB format, how it’s created, its advantages and disadvantages, and how it compares to the PDF format.
What is EPUB?
EPUB, short for Electronic Publication, is an open ebook format created by the International Digital Publishing Forum (IDPF). The format was developed in 2007 as a standard to allow ebooks to be readable across multiple platforms regardless of device or operating system. EPUB quickly became the go-to format for most ebook retailers and libraries due to its flexibility and compatibility.
EPUB is based on standard web technologies like HTML and CSS, meaning it’s structured like a website inside a book format. This allows great flexibility in how the same content is displayed across different devices, from smartphones to dedicated ebook readers like Kindle.
Geek Alert—here’s exactly what’s inside an EPUB file:
XHTML files: The text of the book.
CSS: Controls the design and layout.
Images: Embedded media like illustrations and covers.
Metadata: Provides book details and file structure.
Navigation file: Creates the clickable table of contents.
MIME type: Declares the file type as EPUB.
ZIP: Compresses everything into a single
.epubfile.
That’s right: an EPUB file is actually a zip file. However, this zip file has the .epub extension rather than .zip. While it functions as a compressed archive, EPUB readers are designed to open and interpret its contents for reading.
Write > Convert to EPUB > Distribute
You don’t normally write an EPUB file —rather, the EPUB file is the finished product you create from your source document to distribute to readers (by uploading to Amazon, for example).
There are two basic ways to create an EPUB file for distribution:
Export to the EPUB format from your writing tool (Scrivener, for example; many writing tools offer this).
Use a software tool (like Calibre) to create the EPUB file from your source document (e.g., .docx).
I’ll explain both of these below.
EPUB Advantages
Reflowable text: One of EPUB's biggest advantages is its reflowable text, meaning the text can adjust to fit any screen size. This optimizes the reading experience whether the book is read on a phone, tablet, or e-reader.
Broad compatibility: EPUB is the most widely supported format across ebook retailers and devices, including Amazon, Apple Books, Google Play Books, Barnes & Noble’s Nook, and Kobo. It’s also supported by most library lending platforms.
Supports rich media: EPUB files can include images, audio, video, and interactive elements, making it ideal for textbooks, multimedia-rich ebooks, and children’s books.
Customization: Readers can customize their reading experience by adjusting font sizes, types, and background colors without affecting the core structure of the ebook.
EPUB Disadvantages
Complex Formatting Limitations: While EPUB handles basic text and images well, it can struggle with very complex layouts, such as those found in heavily designed textbooks or books with intricate formatting. This is where fixed-layout formats, such as PDF, might be more suitable.
Consistency Across Devices: Although EPUB is widely compatible, different e-readers and apps may render content slightly differently based on their own interpretation of CSS and HTML, leading to minor formatting inconsistencies. This is rarely a problem, but it does exist.
EPUB vs. PDF
EPUB is better than PDF in almost every way for distributing ebooks, with a few exceptions:
Layout and presentation: EPUB is reflowable, meaning text adapts to the screen size, while PDF is fixed-layout, preserving its original formatting and structure regardless of device or screen size. PDFs are better suited for documents with complex layouts (e.g., textbooks or manuals), but less so for long-form reading on small screens.
Multimedia Support: While both formats can include multimedia elements like audio, video, and interactive elements, EPUB handles them more flexibly, integrating with the flow of the text.
Compatibility: EPUB is widely accepted by ebook retailers, whereas PDFs are more commonly used for manuals, academic papers, or print-ready files, and are less supported by e-readers.
Customizable Fonts and Styles: EPUB allows for the embedding of custom fonts and supports a wide range of CSS-based styles for formatting text, such as headings, footnotes, and lists.
In short: use PDF if you want to preserve a fixed layout; use EPUB for everything else.
NOTE: the latest version of EPUB (EPUB3) also supports fixed layouts, but be sure to verify your distributor supports it. EPUB3 supports fixed layouts for books that require precise positioning, like graphic novels or textbooks.
How EPUB Files are Created
You typically create EPUB files using software tools that package text, images, and formatting into a single file. Some tools combine authoring features with EPUB export; some just do the EPUB creation part.
Some of the most popular tools are:
Calibre: A free, open-source tool that allows users to create, edit, and convert ebooks into different formats.
Scrivener: A writing tool that can export manuscripts directly to the EPUB format.
Adobe InDesign: A professional publishing tool that is commonly used to create complex EPUB files with custom formatting.
Draft2Digital: An ebook distribution platform that includes formatting services. It allows authors to upload a manuscript (DOCX or similar) and automatically converts it into EPUB and other formats. Draft2Digital focuses on easy distribution to multiple retailers.
Sigil: A free, open-source EPUB editor that gives complete control over structure and formatting.
Vellum: An ebook writing and formatting tool specifically designed for self-publishers. It’s particularly known for its easy-to-use interface and high-quality output.
Reedsy Book Editor: An online book editor that allows authors to format and export their books in EPUB format for free.
Which tool should you use?
If you want professional formatting: Adobe InDesign or Vellum stand out. Both offer extensive formatting control and high-quality output.
If you want free or open source solutions: Calibre or Sigil are great choices. Both allow you to create, edit, and convert EPUBs without any cost.
If you want organization + export: Scrivener or Reedsy provide a seamless experience from writing to EPUB export.
If you want simplicity and distribution: Draft2Digital not only handles the EPUB creation process but also automates distribution to major ebook platforms.
Publishers and Distributors That Accept EPUB
EPUB is accepted by nearly all major ebook retailers and distributors, including:
Smashwords (an aggregator that distributes to multiple platforms)
OverDrive (a platform for library ebook lending)
Draft2Digital (another ebook distribution service)
Strategy for Formatting and Distributing EPUB Files
Create in EPUB first: Since EPUB is the most widely accepted format, it’s a good idea to start by creating your ebook in this format. Many tools allow you to easily export EPUB files.
Test Across Devices: Test your EPUB file on different devices (e.g., tablets, smartphones, e-readers) to ensure that it displays correctly across various platforms.
Consider Multiple Formats: EPUB is ideal for most cases (especially text-heavy books), but if you’re creating a book with complex layouts or important visual elements, consider offering a PDF version for readers who prefer a fixed-layout experience.
Summary
EPUB is the most popular ebook format.
Creation: EPUB files can be exported from writing tools (Scrivener) or created using software like Calibre and Adobe InDesign.
Advantages: EPUB offer reflowable text, broad compatibility with nearly all retailers, rich media support, and customizable presentation.
Disadvantages: EPUB struggles with complext formatting, and is best for text-heavy content.
EPUB vs. PDF: EPUB is flexible and reflowable; PDF is fixed-layout, but better for complex designs requiring precise positioning.
Tools: For professional formatting, try Adobe InDesign or Vellum. For free solutions, try Calibre or Sigil.
Best practice: Start with EPUB, test on multiple devices, and offer PDF for complex layouts.