E-book formats compared — EPUB, MOBI, AZW3, FB2 and PDF
Published:
E-books arrive as .epub, .mobi, .azw3, .fb2 or .pdf, and it isn’t always obvious which app will open which. Each format comes from a different history and is supported by different devices.
At a glance
| Format | Origin | Text layout | Main use | Recommendation today |
|---|---|---|---|---|
| EPUB | Open standard (W3C) | Reflowable | Almost all reading apps and stores; Kindle via Send to Kindle | ⭐⭐⭐ The default choice |
| MOBI | Mobipocket → Amazon | Reflowable | Early Kindles | ⚠️ Effectively retired |
| AZW3 (KF8) | Amazon | Reflowable | Kindle devices and apps | Kindle only |
| FB2 | Russian community | Reflowable | Russian and Eastern European apps | Regional |
| Open standard (ISO) | Fixed pages | Print documents, textbooks | Large screens |
EPUB — the universal standard
EPUB is the worldwide standard for e-books. Inside, it is a ZIP file of web pages (one XHTML file per chapter), images and a table of contents. Its text reflows to fit any screen, so it reads well even on a phone.
Apple Books, Google Play Books, Kobo and most other apps support it, and Kindle accepts it through Send to Kindle. For books you create or keep, EPUB is the best choice.
MOBI — the old Kindle format
MOBI was created by Mobipocket and used by early Kindles. Its formatting options are limited, and Amazon’s Send to Kindle no longer accepts it. Convert MOBI files you own with MOBI to EPUB so you can keep reading them in any app.
AZW3 (KF8) — today’s Kindle format
AZW3 is Amazon’s successor to MOBI, supporting modern HTML and CSS. It opens in Kindle devices and apps but in few others. Kindle Store purchases are usually DRM-protected and cannot be converted; DRM-free files convert with AZW3 to EPUB.
Note:
.azwfiles are mostly older DRM-protected Kindle Store books, and current Kindle Store books use yet another format, KFX. Both are designed to be read only on the purchasing account’s Kindle.
FB2 — structure-first XML e-books
FB2 (FictionBook) is an XML format popular in Russia. Rather than describing appearance, it records structure — sections, poems, epigraphs, footnotes — and embeds images in the same file. Few apps outside that region support it, so it is often converted with FB2 to EPUB.
PDF — fixed pages
A PDF is less an e-book than a digital copy of printed pages. Its fixed layout works on tablets and computers but means constant zooming and panning on phones and small e-ink screens. It suits textbooks, papers and comics where layout matters.
Which format should you use?
| Situation | Recommendation |
|---|---|
| Turning your writing or a TXT novel into an e-book | EPUB (TXT to EPUB) |
| Reading on a Kindle | EPUB via Send to Kindle (how) |
| Keeping old MOBI, AZW3 or FB2 files usable | Convert to EPUB |
| Searching or quoting a book’s text | TXT (EPUB to TXT) |
| Layout-heavy textbooks and comics |
About DRM
DRM is copy protection that limits a book to its purchaser. Converting DRM-protected books breaks most stores’ terms and, in many countries, the law — so our converters detect DRM and refuse those files. Public-domain books, your own books and books sold DRM-free convert normally.
Summary
When in doubt, choose EPUB: it opens almost everywhere and can be sent to a Kindle. Converting MOBI, AZW3 and FB2 files to EPUB is the most future-proof way to keep them.