How to Convert EPUB to AZW3 for Free (4 Methods)

AZW3 (also called KF8) is Amazon’s Kindle format for every model made since 2011, and it lays out text much better than the MOBI it replaced. If you’re putting an EPUB on a Kindle by cable, converting it to AZW3 first is what makes it look right. Not sure AZW3 is the one you need? The format comparison settles it in a table.

Here are four free ways to do it, from the one that takes a single click to the one that lets you control every margin.

Method 1: Liber

Liber is an ebook manager that handles the conversion for you. You don’t pick a profile or a format: you pick your eReader once, and Liber works out the rest.

Conversion happens when you send. Connect your Kindle, send the book, and Liber converts it to AZW3 for that model on the way and copies it to the device. The EPUB in your library stays as it is.
You can also convert without sending. One book from its details panel, or a whole selection at once in batch conversion. Both are free.
Same engine as Calibre. Liber converts with ebook-convert, Calibre’s own converter, so the quality is Calibre’s. Liber downloads it for you the first time you convert, so there’s nothing to install. What you skip is the settings.
Wireless delivery is coming with Premium. Sending a book to your Kindle by email, without a cable, will be part of Liber Premium, which isn’t available yet. Until then, delivery is over USB.

Method 2: Calibre

Calibre is the open-source standard for managing ebooks, and its converter is the most thorough there is. The price is an interface with a lot to learn.

Steps:

Install Calibre (Windows, macOS or Linux).
Click Add books and choose the EPUB.
Right-click the book → Convert books → Convert individually.
Set Output format to AZW3 in the top-right corner.
Click OK and wait for the job to finish.
Right-click the book → Open containing folder to find the AZW3.
Copy it to the Kindle’s documents/ folder over USB, or connect the Kindle and use Send to device.

For many books at once: select them all, right-click → Convert books → Bulk convert, set AZW3 as the output format and confirm.

Settings worth knowing:

Page setup → Output profile: choose your Kindle model, so the page and images are sized for its screen.
Look & feel → Styling → Extra CSS: add body { margin: 5%; } if the text runs too close to the edges.
Look & feel → Text → Remove spacing between paragraphs: leave it off if the book separates paragraphs with a blank line instead of an indent.

Quality: excellent. Calibre handles the odd cases that trip up online converters. Downside: you have to install it, and learn your way around a dense interface.

Method 3: Online converters (CloudConvert)

CloudConvert and similar sites convert in the browser, with nothing to install.

Steps:

Go to cloudconvert.com/epub-to-azw3.
Upload the EPUB.
Start the conversion.
Download the AZW3.

Quality: fine for plain novels. Tables, drop caps and complex layouts can come out wrong.

Downsides:

The free plan has a daily limit, so it’s awkward for more than a few books.
No real batch conversion.
Your book is uploaded to someone else’s server, which matters if it’s a private document.

Method 4: ebook-convert (command line)

If you live in a terminal, Calibre ships ebook-convert, and it gives you control over everything.

# Basic conversion
ebook-convert input.epub output.azw3

# Tuned for a specific Kindle
ebook-convert input.epub output.azw3 --output-profile kindle_pw3

# With your own margins and font size
ebook-convert input.epub output.azw3 \
  --output-profile kindle_pw3 \
  --margin-left 8 \
  --margin-right 8 \
  --base-font-size 11

Kindle profiles:

Profile	Device
`kindle`	Original Kindle
`kindle_dx`	Kindle DX
`kindle_pw`	Paperwhite 1st and 2nd gen
`kindle_pw3`	Paperwhite 3rd gen and later
`kindle_voyage`	Kindle Voyage
`kindle_oasis`	Kindle Oasis

Convert a whole folder:

#!/bin/bash
for epub_file in /path/to/epubs/*.epub; do
  base="${epub_file%.epub}"
  ebook-convert "$epub_file" "${base}.azw3" --output-profile kindle_pw3
  echo "Done: $(basename "$epub_file")"
done

Quality: excellent, since it’s Calibre’s engine, and fully scriptable.

Which one to use

Method	Quality	Many books at once	Runs on your computer	Effort
Liber	Calibre’s engine	Yes	Yes	Low
Calibre	Calibre’s engine	Yes	Yes	Medium
CloudConvert	Good for plain text	No	No	Low
ebook-convert	Calibre’s engine	Yes, with scripts	Yes	High

The quality is the same in three of the four: what changes is how much you have to do. If you want conversion and delivery to be one step, Liber is the shortest route. If you want to control every parameter or automate it, ebook-convert is the tool.

Fixing common problems

These are Calibre settings, in the conversion window. With ebook-convert they have equivalent command-line options.

Images look blurry or too small. Check that Page setup → Output profile matches your Kindle, so images are sized for its screen.

The book’s fonts are gone. Under Look & feel → Fonts, tick Embed font family and type the family name exactly as the EPUB’s stylesheet declares it.

The table of contents is missing or broken. Under Table of Contents, tick Force use of auto-generated Table of Contents, so Calibre builds it from the chapter headings.

Paragraph spacing is all over the place. Under Look & feel → Text, tick Remove spacing between paragraphs, so the spacing comes from the indent and not from blank lines mixed into the source.

Getting the file onto the Kindle

Every method except Liber leaves you with an AZW3 on your disk, and it still has to reach the Kindle:

By USB: connect the Kindle, open it as a drive and copy the file into the documents folder.
By email: send it as an attachment to your @kindle.com address. Amazon accepts EPUB directly this way, and converts it on its side.

In Liber, converting and delivering are the same step: choose the book, send it, and it arrives on the connected Kindle already in AZW3.