It's one of the strange, unglamorous truths about eBook publishing. Before your book shows up on a Kindle, iPad, Nook, Kobo or other tablet, it has to first become a digital file that works with those platforms and devices.
Unfortunately, not all eBook formats work the same way. Some are designed for flexible, reflowable reading. Some preserve every visual element exactly where you put it. Some work best for previews, downloads, or direct-to-reader delivery. Others are tied to certain retailers or devices. And there are even some formats that aren't as popular as they once were, yet authors continue to use them as not everyone has the most up-to-date eReader.
For self-publishing authors, understanding eBook formats doesn't have to mean becoming a file expert or having to diagnose, right down to the exact pixel, which file works best. Overall, you want to protect the reading experience, and the best way to do that is to make sure your eBook looks great on a variety of devices.
The truth about eBook formats
Once your book leaves your computer, it has to make it out there in a world where compatibility and layout are paramount. Users will be reading your book on tiny phone screens, large tablets, dark mode and more. They'll make font size adjustments, accessibility changes and more. They'll expect a clickable table of contents, embedded images and fonts, and for the book to open clearly and cleanly the first time.
Most eBooks fall into one of three formats: ePUB, MOBI or PDF. But just knowing the file extensions isn't enough. As a self publishing author, you have to ask yourself, which format should my book actually be in before I distribute it?
There is no single one-size-fits-all eBook format
When indie authors think about publishing, they often think about books that are in print, like paperback and hardback books. When they think of eBooks, they tend to think of a "one size fits all" universal format. Sadly, "eBook format" is not one single thing. It's a whole category that includes multiple file formats, and each format has its own purpose.
The format you choose affects how your book looks, how readers will interact with it, and even which stores can sell it. A poor eBook conversion can cause a ton of problems that print books don't have to deal with, ranging from broken paragraph spacing to missing images, or even a table of contents that doesn't work. The eBook text might be too small for phones or images might shift unpredictably. It's also entirely possible that your eBook looks great on one device and terrible on another.
To make things worse, readers don't separate the writing from the reading experience. If an eBook is hard to read or navigate, or if the layout is messy, it doesn't matter how stellar the writing is. That's exactly why BookBaby's eBook conversion transforms a manuscript into different files that can be read on eReaders, smartphones, tablets and popular devices including Kindle, Apple iPad, and Barnes & Noble Nook.
eBook formatting isn't just a technical step — it's actually a part of the product. So before you dive into eBook conversion, it's important to understand more about the formats you'll be working with, and how they work with a proven publishing strategy.
ePUB: the standard eBook format for authors
If there's one format the self-publishing authors need to understand first and foremost, it's ePUB. ePUB is the standard eBook format used across a variety of devices and platforms. It's flexible, widely supported and made for digital reading.
ePUB's biggest advantage is that it's reflowable (more on how that works below). Simply put, a reflowable ePUB lets readers customize their reading experience. They're able to change the font size, line spacing, margins and sometimes even the font style, depending on their reading app or device.
To get this kind of flexibility, however, authors have to let go of some control. A reflowable ePUB file doesn't look exactly the same on every single screen. Page numbers might shift. A paragraph that appears at the top of one person's e-reader might appear lower on another. The book adapts to the device rather than forcing the device to show the book the same way it is in print.
Best uses for ePUB
If your reading experience relies mainly on text, ePUB will be the ideal choice. It typically covers:
- Novels
- Memoirs
- Short story collections
- Narrative nonfiction
- Business and self-help books
- Personal development books
- Poetry collections
- Most chapter-based books
ePUB books are also able to easily handle images, links, tables of contents, headings, footnotes and other common book elements. ePUB works best when the design itself doesn't depend on every single visual element staying in one exact place.
At BookBaby, our ePUB eBook formatting is designed to make your book look its best across phones, tablets and eReaders. Formatting your book to look great across devices is the most important part. Your reader might not be using a dedicated eReader in a quiet room. They might be reading on their phone during lunch, or on a tablet at night before bed. ePUB is flexible enough to support both of those needs and everything in between.
MOBI: the older Kindle format
When it comes to Kindle publishing, you'll likely hear about the MOBI format. In the past, MOBI was strongly associated with Amazon Kindle. For years, authors and publishers alike needed MOBI files for Kindle compatibility. You'll still hear authors talking about MOBI because it used to be a vital part of preparing one's eBook for reading on Kindle.
The good news is that Amazon has moved away from relying on MOBI the way it used to, and modern Kindle eBook conversion often involves ePUB uploads that Amazon then converts on its end to better reading specifically on a Kindle device.
Thankfully, you don't need to worry about MOBI the way authors did years ago, but you should still understand where it comes from when you hear it come up in publishing conversations. Also, although BookBaby offers eBook conversion services to MOBI format, if you specifically need to convert from ePUB to MOBI file we provide instructions on how to convert from ePUB to MOBI if necessary.
AZW and AZW3: Kindle-compatible formats
AZW and AZW3 are formats designed specifically for the Amazon Kindle. Although you might not directly create or upload these types of files, they're worth mentioning in this guide because your readers might discover them when downloading or reading a Kindle-specific eBook.
AZW3 is also known as Kindle Format 8. It offers more advanced formatting than the older MOBI files did. AZW3 can handle richer design elements, better typography and more complex layouts than its older Kindle cousin. Oftentimes authors don't need to specifically build their AZW3 files from scratch, you just have to make sure that your source file is clean enough to convert properly.
For instance, if your Word document is full of manual spacing, inconsistent headings, random tabs, pasted-in formatting or uncompressed images, the conversion process can get messy, quick. A clean source file gives you a much cleaner eBook.
If you want to sell on Kindle, the eBook conversion specialists at BookBaby can turn your manuscript into ePUB, MOBI or AZW3 formats for eReaders, smartphones, tablets and other popular eReaders.
PDF: the useful and familiar format
Nearly everyone who has ever used a computer knows what a PDF file is. PDF files have been around since 1993 and were designed to make documents look consistent across different computing platforms. PDFs can be the best choice for certain types of books, including:
- Workbooks
- Downloadable bonuses
- Media kits
- Advanced reader copies
- Press materials
- Lead magnets
- Design-heavy guides
- Printable worksheets
If you're giving readers a downloadable checklist, planner, workbook, or a printable guide, PDF is perfect for the job. Readers expect to view and print it exactly as designed, and that's the kind of ease of use that PDF formats offer.
However, if you're selling a novel or nonfiction book through eBook retailers, PDF alone usually isn't enough. It also isn't designed to deliver a consistent reading experience across devices (remember, it was made before eReaders were even a thing).
That can sometimes confuse self-publishing authors since they see that their PDF looks great and assume it will look equally great on other devices. Even a professionally designed PDF may need to be converted to ePUB for proper eBook distribution.
BookBaby accepts PDF files for eBook conversions, but for best results, we recommend uploading a Microsoft Word document.
Reflowable vs. Fixed Layout: which should you choose?
You might be surprised to learn that the most important eBook formatting decision has nothing to do with ePUB vs. PDF or Kindle vs. Apple. It has to do with reflowable vs. Fixed Layout.
Reflowable eBooks let text adapt to the screen. Most ePUB files for novels and standard nonfiction books are reflowable. Conversely, a Fixed Layout eBook preserves the exact placement of text and images. It looks and functions more like a designed page. This difference is particularly important since different kinds of books need different kinds of reading experiences.
For example, a 300-page thriller doesn't need every line to show up in the exact same place on every device. Forcing such a layout would end up making the book harder to read. However, a children's picture book, a cookbook, a photography book or a graphic novel may depend on text and images appearing together in a specific way. Reflowable text might break the design if it's used in cases like that.
When reflowable is best
Reflowable books are the standard chosen by most self-publishing authors who are writing standard fiction or nonfiction. With reflowable eBooks, the format prioritizes readability over the exact page design. Readers decide how large the text should be, what orientation they prefer reading in, and how the content fits to their device. For novels and chapters, this makes perfect sense.
The best way to take advantage of the reflowable layout is to format your manuscript properly before it's converted. That means clean headings, consistent paragraph styles, working links, a functional table of contents, and correctly inserted images.
eBook conversion is less about flipping a switch and having your manuscript look instantly beautiful across devices, and more like a step-by-step translation where our team is essentially translating from one type of file to another. The cleaner the original is, the better the results will be.
When Fixed Layout is best
With a fixed layout eBook, the page is more controlled. Your images, captions, text boxes and other design elements stay in their specific places. But fixed layout formatting also has trade-offs.
They may not be supported on every device or platform, and depending on the details, they may cost more to produce. They don't give readers the same kind of experience as reflowable eBooks, and that in turn can limit distribution options depending on the retailer and the device.
With BookBaby, our fixed layout eBook formatting service uses high-resolution PDF files that are converted into eBooks designed for both the Amazon Kindle and the Apple Books app. We do not currently produce fixed layout files for the Barnes & Noble Nook tablet. If you're planning to release a book that needs a fixed layout, you'll want to plan your distribution closely around the platforms that best support that type of format.
If you're still trying to decide on fixed layout versus reflowable, we recommend using a fixed layout when the design is part of the content itself, such as with:
- Children's books
- Illustrated books
- Photography books
- Cookbooks
- Graphic novels
- Comics
- Art books
- Textbooks
- Diagram-heavy manuals
- Books that include complex charts or tables
What files you should submit for eBook conversion
Before your eBook becomes an ePUB, MOBI, AZW3, PDF, or Fixed Layout file, you start with a source file. This is the manuscript or the design file that you upload for conversion. At BookBaby, we accept a variety of file types, including Microsoft Word documents, PDFs, InDesign files, and ePUB files, with Microsoft Word being the preferred format.
Word documents
Why are Word docs the preferred choice? Simply because they're the easiest and most practical to format. A clean Word file looks beautiful when it's converted properly for both fiction and nonfiction. So what exactly do we mean by clean? That means:
- Using paragraph styles instead of manually formatting everything
- Avoiding spaces or tabs to create indents
- Using proper page breaks between chapters
- Using consistent heading styles
- Avoiding text boxes unless absolutely necessary
- Inserting images properly
- Not forcing print-style formatting into the file
Your Word document isn't supposed to look like a designed print book. Instead, it works best when it's laid out with structured content that makes it easier and faster to convert.
PDF source files
We accept PDFs for conversion, but they're not ideal as the source file for standard reflowable eBooks. PDFs lock the layout, which makes it harder to extract clean, flexible text. If your goal is to have a fixed layout eBook, a high resolution PDF is exactly what you want to submit. In fact, we recommend supplying a high-resolution PDF with all fonts embedded and links activated for the best possible fixed layout eBook conversion.
In short, PDF is perfect if you want your eBook to preserve the existing layout. That's very different from uploading a PDF as the source file for your reflowable eBook.
InDesign files
Adobe InDesign files are commonly used by professional book designers. If your book has already been laid out for print or digital publication by a book designer, they may provide you with an InDesign file. This format can be useful for complex books, but it also depends on how the file itself was made. A print-focused InDesign file might still need to be adjusted for a digital eBook conversion.
If you're a self-publishing author currently working with a designer for your book, it's a good idea to ask them early, "Will this file also work for eBook conversion?" Don't wait until the print layout is done to think about how you're going to format the book for digital use.
ePUB source files
Some authors will already have an ePUB file and simply need to upload it in order to distribute it. We accept ePUB files for either conversion or processing. At the same time, having an ePUB file doesn't automatically mean your book is ready for distribution. It still has to validate properly, display well, and meet certain retailer requirements.
A homemade ePUB file can look great on one device and fail on another, which is why testing is so important. If you choose BookBaby as your eBook conversion platform, you'll be glad to know that we test your eBook layout and formatting on a variety of devices so you don't get the shock of a lifetime when your book loads and looks like a garbled mess!
Cover file formats
Authors often focus on getting the interior part of the eBook looking great, but then forget that the cover also has technical requirements. Just like the inside of the book, your cover has to display properly too, since it's going to be the image that's shown in online stores, search results, reader libraries, thumbnails and on device screens.
We recommend that dynamic eBook covers be in either JPG or PNG format. They should use RGB color and be vertical rather than square. Your cover file should also include the book title and author name.
Your eBook format is part of the reader experience
Your eBook format isn't just the technical "container" for your book. It shapes how your book is experienced and enjoyed. For self-publishing authors, that means that formatting and conversion are all rolled into the art and craft of publishing.
Of course, you don't need to know every single specific technical detail about how ePUB, MOBI, AZW3 or PDFs work, but you should understand what each format is for, where it works best, and how your decision will affect your eBook's distribution.
Remember, ePUB is ideal for text-driven books and gives readers the most flexibility. MOBI and AZW formats are associated with Kindle and PDF preserves the layout, but it's not always the best for retailer-specific eBook reading (like Nook and other eReaders).
Don't forget that a clean source file leads to a clean eBook conversion leads to a superior reading experience. Self-publishing your eBook is a great way to stay in control of the features and design parts that make your eBook unique, but control doesn't mean doing everything blindly. You'll want to make informed choices about your book long before it ever reaches an online marketplace.
But when your eBook finally gets downloaded and opened on a device for the first time? Readers won't care what file type it is. They'll see that it's clean, properly formatted, and feels good to read, and that's what matters most.
Get started with BookBaby.com today and get a free, no obligation quote for your eBook conversion. Ask us about eBook distribution too and make your book visible on Amazon, Apple Books, Barnes & Noble and more.
TLDR
Understanding eBook formats is a critical part of self-publishing because the file type directly affects how readers experience your book across devices. ePUB is the industry-standard format for most fiction and nonfiction because it offers flexible, reflowable text that adapts to different screen sizes and reader preferences. MOBI and AZW formats are associated with Amazon Kindle devices, while PDFs preserve exact layouts and work best for fixed-format content like workbooks, comics, cookbooks, and design-heavy guides. Authors should also understand the difference between reflowable and Fixed Layout eBooks, since each serves different reading experiences. Clean source files, especially properly formatted Word documents, lead to smoother eBook conversion and better compatibility across retailers and devices. BookBaby helps self-publishing authors convert manuscripts into professional eBook formats optimized for Kindle, Apple Books, Nook, Kobo, tablets, smartphones, and other modern reading platforms.