EPUB, MOBI, and PDF do different jobs, and using the wrong one costs you sales or a clean reading experience. Here's what each format is for, which retailers require which, and how to cover them all.
Key Takeaways
- EPUB is the universal ebook standard and what nearly every retailer now wants, including Amazon, which converts it on upload.
- MOBI is Amazon's legacy format and is effectively retired, KDP no longer accepts MOBI for new uploads. Use EPUB instead.
- PDF is a fixed-layout, print-oriented format. It's right for print interiors and some fixed-layout books, but a poor choice for standard ebooks.
- Reflowable formats (EPUB) adapt to any screen; fixed-layout formats (PDF) keep an exact design, the choice depends on your book type.
- Want every format delivered correctly in one package? Call Spines Publishing USA at (708) 575-4611 or email info@spinespublishingusa.com.
Authors are often confused about ebook file formats, and the landscape has shifted in recent years. Pick the wrong format and your book either won't upload, won't reflow correctly on readers' devices, or won't look the way you intended. Here's a plain-English guide to EPUB, MOBI, and PDF, what each is built for, and which you actually need in 2026.
What Each Format Is Built For
EPUB — The Universal eBook Standard
EPUB is the open, industry-standard ebook format, and in 2026 it's what you should reach for by default. It's reflowable: text adapts to any screen size and the reader's chosen font and size. Virtually every retailer accepts EPUB, Apple Books, Kobo, Barnes & Noble, Google Play, and library platforms, and Amazon now accepts EPUB directly and converts it to its own format on upload.
MOBI — Amazon's Retired Legacy Format
MOBI was Amazon's original Kindle format, but it's effectively obsolete. Amazon has phased it out: KDP no longer accepts MOBI files for new uploads, and Send-to-Kindle dropped MOBI support. If you have old MOBI files, convert them to EPUB. You almost never need MOBI in 2026.
PDF — Fixed-Layout and Print
PDF is a fixed-layout format: it preserves an exact page design regardless of device. That makes it the correct format for your print book interior and for some highly designed fixed-layout ebooks (children's picture books, cookbooks, art books, complex non-fiction). But for a standard novel ebook, PDF is a poor reading experience, it doesn't reflow, so readers must pinch and zoom on small screens.
| Format | Type | Best For | Status in 2026 |
|---|---|---|---|
| EPUB | Reflowable | Standard ebooks, all retailers | The default standard |
| MOBI | Reflowable (legacy) | Old Kindle files | Retired, use EPUB |
| Fixed-layout | Print interiors, fixed-layout books | Essential for print, not standard ebooks |
Which Retailers Require Which Format
- Amazon KDP (ebook): Accepts EPUB (recommended), and converts it on upload. No longer accepts MOBI.
- Amazon KDP (print): Requires a print-ready PDF interior plus a PDF cover.
- Apple Books, Kobo, Google Play, Barnes & Noble: EPUB.
- Library platforms (OverDrive, etc.) via aggregators: EPUB.
- IngramSpark (print): Print-ready PDF interior and cover; EPUB for ebook distribution.
The short version: you need a clean EPUB for ebook everywhere, and a print-ready PDF for paperback/hardcover. MOBI is no longer part of the picture.
Reflowable vs. Fixed-Layout Formatting
This is the core distinction that determines which format fits your book.
Reflowable (EPUB) means the text flows to fit whatever screen and font size the reader chooses, ideal for text-driven books (novels, most non-fiction) where the words matter more than the exact page design. The reader controls the experience.
Fixed-layout (PDF, or fixed-layout EPUB) locks the design in place, every element stays exactly where you put it. This is essential when layout carries meaning: children's picture books where text wraps around art, cookbooks with precise recipe layouts, or heavily illustrated non-fiction. The trade-off is that fixed-layout doesn't adapt to small screens as gracefully.
Choose based on your book: if it's mostly words, go reflowable EPUB. If the visual layout is part of the content, you'll need fixed-layout, and likely a print PDF too. Getting this wrong is a common error, see common formatting mistakes.
How Spines Delivers Every Format in One Package
Most authors need at least two files, a reflowable EPUB for ebook retailers and a print-ready PDF for paperback, and possibly a fixed-layout file if their book is illustration-heavy. Producing each correctly, to each platform's specs, is fiddly and error-prone when done piecemeal.
Spines Publishing USA's formatting service delivers all the formats your distribution plan requires from a single, coordinated process: a clean EPUB built with proper styles and a linked table of contents, and a print-ready PDF formatted to your exact trim size and margins (see our KDP formatting checklist). One source, every format, all upload-ready.
Need every format, done right?
Spines Publishing USA produces print-ready PDF and retailer-ready EPUB files from one coordinated process, formatted to each platform's exact specs. Call (708) 575-4611, email info@spinespublishingusa.com, or explore book formatting.
Explore Book FormattingThe format question is simpler than it looks in 2026: EPUB for ebooks everywhere, print-ready PDF for paperback and hardcover, and fixed-layout only when your book's design demands it. MOBI is history. Match the format to the job and your book reads beautifully on every device and uploads cleanly to every retailer.
Frequently Asked Questions
What's the difference between EPUB, MOBI, and PDF?
EPUB is the universal, reflowable ebook standard accepted by virtually all retailers. MOBI is Amazon's retired legacy Kindle format, no longer accepted for new uploads. PDF is a fixed-layout format ideal for print interiors and highly designed books but a poor choice for standard reflowable ebooks.
Do I still need a MOBI file in 2026?
No. Amazon has phased out MOBI, KDP no longer accepts it for new uploads and Send-to-Kindle dropped support. Use EPUB instead; Amazon converts it to its own format on upload. If you have old MOBI files, convert them to EPUB.
Which ebook format does Amazon KDP require?
For ebooks, KDP recommends and accepts EPUB, which it converts to its own Kindle format on upload. For print books, KDP requires a print-ready PDF interior and a PDF cover. MOBI is no longer accepted.
What's the difference between reflowable and fixed-layout?
Reflowable formats (EPUB) let text adapt to any screen size and reader-chosen font, ideal for text-driven books like novels. Fixed-layout formats (PDF or fixed-layout EPUB) lock the exact design in place, essential for picture books, cookbooks, and heavily illustrated titles where layout carries meaning.
Which format should I use for my novel?
For a standard, text-driven novel, use a reflowable EPUB for ebook retailers and a print-ready PDF for paperback and hardcover editions. You don't need MOBI, and you should avoid distributing a plain PDF as your ebook because it won't reflow on small screens.
