You get a MOBI file for older Kindles and other MOBI-only readers, with the cover, chapters and contents list carried over from your EPUB.
To convert EPUB to MOBI, add the EPUB file, keep MOBI as the output format and download the result. The output is the old MOBI 6 type, which older Kindles and MOBI-only readers open when you copy the file over a USB cable. A recent Kindle usually does better with the EPUB itself, so check that before you convert. In our test a 20.4 kB EPUB became a 51.5 kB MOBI with its cover and all 5 contents entries, though other books will differ, and a DRM-protected EPUB cannot be converted at all.
Transfers use HTTPS, and files converted on the free tier are deleted after 24 hours, so the result is not a long-term archive. Quality depends on the source file, so open the MOBI file once before you share it.
EPUB (Electronic Publication)
An open ebook standard maintained by the W3C. An EPUB is a ZIP package of XHTML chapters, stylesheets, images and a navigation file, and its text reflows to fit the screen and the reader's chosen font and size.
MOBI (Mobipocket eBook)
The ebook format Mobipocket started and Amazon took over. This page writes the old MOBI 6 layer, which has little styling and no custom fonts, and it is the type that Kindle 1, 2 and DX class devices and other MOBI-only readers can open.
A 20.4 kB sample EPUB made by us (cover, 3 chapters, 5-entry contents, 2 images), converted on indox.org
In our test Calibre's metadata reader showed the title, author and language of the MOBI, and the cover was kept as a 21.6 kB JPEG with a thumbnail. A second test book that had no cover came out with a generated one.
The sample had a 5-entry nested contents list, and all 5 entries were still there, at the same depth, when we converted the MOBI back to EPUB with calibre 6.13.0. A second test book kept 2 of 2.
PNG with transparency, JPEG and GIF images all came out as JPEG in our tests. The MOBI held 4 JPEG records: the cover, its thumbnail and 2 figures.
The output file names calibre 6.13.0 as the tool that wrote it. We did not change any settings in our run, so the result is Calibre's default type, the old MOBI 6 format.
| Your reader | Use | Why |
|---|---|---|
| Kindle 1, 2 or DX class, loaded by USB | MOBI from this page | Forum posts report these models read only the old MOBI type |
| A recent Kindle | The EPUB, via Send to Kindle | Amazon reportedly accepts EPUB there; confirm on Amazon's site |
| A modern Kindle where layout matters | AZW3, made with a desktop tool | It carries the KF8 layer with HTML5 and CSS3 |
| Publishing a book on KDP | EPUB | KDP ended MOBI for reflowable books on 1 August 2021 |
| Fixed pages for print or screen | EPUB to PDF | A PDF keeps page positions that MOBI 6 cannot |
Drop the EPUB on the box or choose it from your device. Keep the original, because it is the better-quality copy and the one modern readers prefer.
Check that MOBI is the output format, start the conversion and wait for it to finish. In our test a 20.4 kB book took 5.8 seconds from the click to Completed.
Save the file, connect your Kindle or reader by USB and copy it into its documents folder. Then open it and check the contents list and the pictures.
You hand over an EPUB and take back a MOBI for an older Kindle or reader, without installing Calibre. The page states the output type, what it drops and where a different route is better.
The upload box shows the live size limit before you add a file. Signing in raises it; a paid plan does not change it.
EPUB in, MOBI out. Pick another output on the converter if you need a different format.
Files are encrypted in transit over HTTPS and processed on indox infrastructure.
Free-tier files are kept for 24 hours after the job finishes, then deleted automatically.
| What you see | Why | What to do |
|---|---|---|
| The Kindle does not list the MOBI | Newer Kindles and Send to Kindle may no longer take MOBI | Copy the file by USB into the documents folder, or send the EPUB instead |
| The conversion fails | The EPUB may be DRM-protected or damaged | Use a DRM-free copy you own, or try another copy of the file |
| Table borders or note styling are gone | Old MOBI 6 has little styling support | Keep the EPUB for layout, or use EPUB to PDF for fixed pages |
| You cannot change the font on a newer Kindle | Forum users report old MOBI 6 files lack custom font support | Send the EPUB or make an AZW3 with a desktop tool |
Ebooks with fixed pages
Convert EPUB files to AZW3 format.
Convert EPUB files to DOCX format.
Convert EPUB files to EPUB format.
| Compared on | EPUB | MOBI |
|---|---|---|
| Standard | Open standard maintained by the W3C | Proprietary, partly documented; no public specification |
| Container | ZIP package of XHTML, CSS and images | Binary PalmDB file; Mobipocket first, then Amazon |
| Styling | Full HTML and CSS support, embedded fonts | Old MOBI 6 has little styling; KF8 added HTML5 and CSS3 in 2011 |
| Where it opens | Most readers and apps, and Send to Kindle | Older Kindles and MOBI-only readers; Kindles still read it over USB |
| Publishing | Accepted by Amazon KDP | KDP ended MOBI for reflowable books on 1 August 2021 |
Facts checked on November 4, 2026
No tool matches that search.
Probably not if your Kindle is recent. Amazon reportedly changed Send to Kindle in late 2023 to accept EPUB and drop MOBI, though we could not verify Amazon's current wording ourselves. MOBI is mainly for older models and MOBI-only readers that you load by USB.
MOBI 6 is the old layer with little styling. AZW3 carries the newer KF8 layer with HTML5 and CSS3, so it keeps more of the layout. This page writes MOBI 6 only. For a modern Kindle, use the EPUB itself or make an AZW3 with a desktop tool such as Calibre.
Text, chapters, cover and the contents list did in our test. Table borders, note-block styling and image transparency did not. The result suits plain novels and non-fiction better than books with heavy design.
Newer Kindles and Send to Kindle may refuse MOBI. Copy the file by USB into the documents folder instead, or send the EPUB. A DRM-protected source will have failed to convert in the first place.
In our test, yes. The cover was a 21.6 kB JPEG, 5 of 5 contents entries survived with their nesting, and a book with no cover got a generated one. Check your own file, because other books can behave differently.
No. A book with copy protection cannot be read by the converter. Use a DRM-free EPUB that you own.
In our anonymous test there was no sign-up and no limit message. A 20.4 kB EPUB took 5.8 seconds from the click to Completed and a 4.5 kB one took 4.8 seconds. Larger books will take longer.
They are re-encoded as JPEG, so PNG transparency and GIF animation are lost and fine lines can soften. In our test 4 images in the output were all JPEG.