EPUB vs MOBI: What’s the Difference for Kindle?
By Andrew Butson · July 2, 2026 · 6 min read
For nearly everyone today, EPUB is the format to use: it’s the open standard almost every e-reader supports, and Amazon itself has moved away from MOBI, now accepting EPUB directly for Kindle rather than asking you to convert to its own older format first.
MOBI isn’t really a live alternative any more so much as a legacy format from Kindle’s early years. If you’re not already sitting on a library of old .mobi files, there’s no reason to seek the format out.
EPUB and MOBI both hold reflowable e-books, but they come from opposite traditions. EPUB is an open standard, maintained publicly and built on ordinary web technologies (XHTML and CSS), which is why the vast majority of e-readers, apps and bookshops support it. MOBI began life as Mobipocket’s proprietary e-book format, was acquired by Amazon in 2005, and became the format the original Kindle read when it launched in 2007. It was a closed, single-vendor format tied to one company’s devices.
That history matters because it explains where each format stands today. EPUB kept evolving as an open standard used everywhere; MOBI stayed tied to Amazon’s own roadmap, and Amazon has since moved on from it.
It’s worth being precise about what "MOBI" even means, since the name gets used loosely. Strictly it refers to the old Mobipocket-derived file structure; Amazon’s later Kindle-native format is a different, more capable design that a lot of people still casually call "MOBI" out of habit. Either way, neither is an open, publicly documented standard the way EPUB is. Both remain tied to Amazon’s own ecosystem rather than being something any reading app can freely implement from a public spec.
| EPUB | MOBI | |
|---|---|---|
| Standard | Open (IDPF / W3C) | Proprietary — originally Mobipocket, later Amazon |
| Built on | XHTML and CSS (zipped) | Proprietary binary structure |
| Device support | Most e-readers, phones, apps, bookshops | Historically Kindle only |
| Amazon’s current stance | Now accepted directly via Send-to-Kindle | Deprecated / legacy |
| Succeeded by (on Kindle) | N/A — still current | KF8 / AZW3, Amazon’s newer format |
| Reflow, fonts, accessibility | Modern support (EPUB 3) | Limited, older feature set |
| Morphr support | Converts to/from PDF, TXT, MD, HTML, DOCX | Not supported — see below |
Two Kindle-era formats, one of which moved on
When the first Kindle launched in 2007, it read MOBI, a format Amazon had inherited when it bought the e-book company Mobipocket two years earlier. For a while that made sense: Kindle was the dominant e-reader, and MOBI was its native tongue. EPUB, meanwhile, was doing the opposite thing: being adopted as an open standard by essentially every other reading app and bookshop, from Apple Books to Kobo to Google Play Books, precisely because no single company controlled it.
Amazon’s own hardware eventually outgrew MOBI’s limitations. It introduced a newer format, generally known as KF8 or AZW3, that supported far more modern typography, layout and formatting than the older MOBI spec ever could. MOBI didn’t disappear overnight, but it stopped being the format Amazon was building toward. It became the thing Kindle grudgingly still understood, not the thing it was designed around.
Why MOBI faded
The short version is that Amazon didn’t need its own closed format once it decided it no longer benefited from one. As EPUB matured into a genuinely capable standard, with embedded fonts, real CSS layout, accessibility metadata and support for right-to-left scripts, the case for keeping a proprietary Kindle-only format got weaker. In recent years Amazon has leaned into accepting EPUB directly through its Send-to-Kindle service rather than requiring people to convert their books to MOBI first, and MOBI itself has been quietly retired from the front of that process. The precise cut-off details have shifted more than once as Amazon has rolled the change out, so it’s more useful to know the direction of travel than to memorise a date: MOBI is legacy, EPUB (and Amazon’s own newer KF8/AZW3) is where things have landed.
What this means for Kindle owners today
In practice, if you have an EPUB you want on a Kindle, you no longer need to hunt for a MOBI converter at all: current Kindle apps and the Send-to-Kindle service accept EPUB files directly and handle the conversion internally. That’s a meaningful simplification: fewer format conversions means fewer chances for footnotes, images or formatting to go wrong along the way. The only people who still have a real reason to think about MOBI are those sitting on an existing library of old .mobi files, or using genuinely old Kindle hardware or software that predates EPUB support. Even then, the practical fix is usually to update the app or re-send the book as EPUB rather than to keep producing more MOBI files.
What Morphr does and doesn’t convert
To be straightforward about it: Morphr does not convert to or from MOBI. It’s a closed, proprietary format without an openly documented specification to build a reliable, from-scratch encoder against, which doesn’t fit a tool built entirely on open formats processed locally in your browser. What Morphr does convert, in both directions where it makes sense, is EPUB: to and from PDF, plus TXT, Markdown, HTML, DOCX, RTF and ODT. For the common real-world need, such as getting a book onto a Kindle or getting a book out of EPUB into something else entirely, that covers the format that actually matters today. If you specifically need an old .mobi file converted, a Kindle app’s own Send-to-Kindle EPUB upload is the more reliable path than looking for a MOBI-specific converter.
Reach for EPUB when…
- You want a book to work across Kindle, Kobo, Apple Books and just about anything else.
- You’re self-publishing or archiving and want a format that won’t depend on one company’s continued support.
- You want to send a book to a Kindle today — Send-to-Kindle now accepts EPUB directly.
- You need modern typography, embedded fonts or accessibility features that older MOBI never supported.
MOBI is only worth thinking about when…
- You already have an existing library of old .mobi files you need to keep reading.
- You’re using genuinely old Kindle hardware or software that predates EPUB support.
- Otherwise, there’s no practical reason to seek MOBI out for a new book today.
Morphr doesn’t convert to or from MOBI, but it does convert EPUB to PDF (and TXT, Markdown, HTML, DOCX) locally in your browser.
Runs entirely in your browser — nothing is uploaded.
Frequently asked questions
- Does Kindle still use MOBI?
- Not as its focus. Amazon has moved on to a newer format (often called KF8 or AZW3) and now accepts EPUB directly through Send-to-Kindle, so MOBI has become a legacy format rather than the one Kindle is built around.
- What replaced MOBI on Kindle?
- Amazon’s own newer format, generally referred to as KF8 or AZW3, which supports far more modern layout and typography than MOBI did. Increasingly, though, Amazon simply accepts EPUB directly rather than requiring a Kindle-specific format at all.
- Can Morphr convert a file to or from MOBI?
- No. MOBI is a closed, proprietary format without an open specification, so Morphr doesn’t support it. It does convert EPUB to and from PDF, TXT, Markdown, HTML, DOCX and other open formats.
- How do I get an EPUB onto my Kindle now?
- Send it through Amazon’s Send-to-Kindle service or app: current versions accept EPUB files directly and handle the conversion internally, so there’s no need to produce a MOBI file yourself first.