Size: free software to manage, convert and send your ebooks

Last updated on 29 October 2026

You have e-books everywhere. Public domain classics downloaded for the class, some EPUB purchased online, course PDFs, a novel received as a gift. A Kobo e-reader at the CDI, a Kindle at home. And half of the files refuse to open where you need them.

You need Size. I have been using this free and open source software for many years. A fellow traveller who has lost none of his relevance and philosophy over the past few years. This is the tool I open as soon as a file refuses to be displayed on a e-reader. It has evolved a lot since the first version of this article. Here’s what it does today, and what you need to know before installing it.

 

The best application to manage e-books

Calibre is a free and open source e-book management software. It is developed by Kovid Goyal and a community of contributors. He does four things: store your ebooks, convert them from one format to another, send them to your e-reader and read them on your computer.

The main thing at a glance:

• Price : free of charge, without advertising. The project lives on donations.
• Account : None.
• Systems : Windows 10 (version 1809 or later), macOS and Linux. A portable version for Windows is installed on a USB stick.
• Language : interface in French.
• Current version : 9.16, released on 9 October 2026.

Old computers are not forgotten. The site offers old versions compatible with Windows 10 before 1809, with Windows 8 and with Windows 7, without losing your books or settings. Convenient for a computer room that has not been renewed for a long time.

A library for all your eBooks

This is the basic function, and it is already a lot. You drag your files into the Calibre window. The software stores them in a library on your computer. He will search online for the missing information: title, author, publisher, ISBN, abstract, cover.

You can then sort by author, series, label, language or date added. You can also create virtual libraries, one for your 4th grade class and one for your personal readings for example. Search works in the full text of all your books, not just in titles. Since version 9.6, its results are displayed as maps with covers.

Calibre 9 has also added a "shelf" view that presents your books by the slice, stored on shelves. On paper, it is a gadget. In use, for a library of a few hundred titles, it is rather pleasant to find a book at a glance.

A magic reel to convert an ebook from one format to another

It was the function that saved me most of the time. Calibre converts just about everything to just about everything: EPUB, AZW3 (Kindle), KEPUB (Kobo), PDF, DOCX, TXT, HTML and many others.

During the conversion, you can change the layout: font, text size, margins, rowing, table of contents. For PDFs, a dedicated engine automatically locates and removes headers and footers. The text finally becomes legible on an e-reader. On complex PDFs (columns, tables, diagrams), the result remains imperfect. We should not expect miracles.

One point has changed since 2022: the MOBI format is outdated. Calibre has also replaced the MOBI with the AZW3 as the default format for Kindle, with all Amazon e-readers of the last decade supporting it. If you start from scratch, work in EPUB. It is the standard format, readable almost everywhere.

Calibre also integrates an ebook publisher to correct a shell or retouch a table of contents. And if you start from a Word document, the conversion to EPUB works well, provided you have used heading styles in your document.

Size and Kindle: send your books to an Amazon e-reader

This is the question that comes up most often. There are two methods.

With a USB cable. Connect the Kindle: Calibre recognizes her. Select a book and click on ‘Send to device’. Calibre converts the file to AZW3 if necessary. Recent Kindles, which connect differently from older models, are supported.

By e-mail, with Send to Kindle. Each Kindle has its own email address, and Calibre can send a book directly to that address. Two adjustments must be made once:

• in the Calibre preferences, enter your Kindle address in the section dedicated to sharing books by e-mail;
• in your Amazon account, under the heading ‘Manage your content and devices’, add your shipping address to the list of approved emails.

Send from EPUB. Send to Kindle accepts this format and converts it for the reader. The MOBI is now refused. The book arrives in your Kindle library, without cable.

Another novelty on the Amazon side. Since January 20, 2026, DRM-free ebooks purchased from the Kindle Store can be downloaded as EPUB or PDF. There are conditions. Books borrowed via Kindle Unlimited are excluded, even without DRM. For titles published before 9 December 2025, the publisher must activate the title-by-title option. Most books in the store remain protected by default. But when downloading is possible, the file enters Calibre without difficulty.

Caliber and Kobo

Good news for Kobo e-readers. Since version 8, Calibre reads, modifies and natively converts the Kobo KEPUB format, and automatically transforms your EPUBs into KEPUBs at the time of sending. You no longer need an additional extension.

Read and listen to your books on the computer

Calibre integrates its own e-reader. It handles highlighting, notes and search. Since version 9.11, your annotations are also exported as a standalone web page, which can be consulted in any browser. Convenient to keep track of his reading notes.

The e-reader can also read the text aloud. The neural voices of the Piper engine work locally, without going through an online service. Version 9.16 adds Kokoro voices, more natural, with a particularly marked gain in English. For a student who needs to listen to a text by following it with their eyes, it is a serious and free track.

If you are just looking for a lighter computer e-reader, Thorium Reader remains a very good option. To read on a phone, see our selection ofapps to read books on smartphone or tablet. And to turn an EPUB into an audio file, there is DocsToAudio.

AI arrives in Calibre, and it remains optional

Since autumn 2025, Calibre has been offering artificial intelligence functions. You can select a passage in the e-reader and ask for an explanation. You can also discuss an entire book in your library, ask what to read next, or generate a cover.

The important point: all this is optional. No AI-related code is loaded until you have configured a provider, and a setting hides all these functions from the interface. You choose the service: Google, OpenRouter, Anthropic, or a model installed on your computer with Ollama or LM Studio.

My opinion: this is well thought out, but should be handled with caution. With an online service, the extracts you submit leave with the provider. For use with students, I would only activate it with a local model. And frankly, this is not Calibre’s real added value.

Classroom and CDI size

Some practical uses:

• Set up a free reading fund. Recover classics from the public domain with our list of sites to download books for free. Store them by level or sequence, then send them to the facility’s e-readers. For the FLE, the TV5World Digital Library is a good source.
• Manage a fleet of e-readers. With a single Calibre library and one label per class, you load the same titles on each device with just a few clicks.
• Adapt a text. When converting, you can enlarge the font, increase the rowing or widen the margins. It is not a tool designed for dys students, but it is a first step. To go further, DysFacile is designed for that.
• Disseminate your own documents. A collection of texts in Word becomes a clean EPUB, with table of contents, that students read on e-reader, tablet or phone.
• Have pupils create books? Calibre is not made for this. For a creative project in class, Book Creator will be more suitable.

What I like / What I like less

What I like

• Free, free, without account and without advertising.
• Conversion, which solves most format problems.
• Support for almost all e-readers, with Kindle and Kobo in mind.
• A very active development. This summer, a new version was released every two to three weeks.
• AI functions that can be ignored or completely hidden.

What I like less

• The interface is dense. The first few minutes can be a little intimidating.
• There is no official mobile app.
• Calibre does not read DRM-protected books. A book locked by its publisher remains a prisoner of the seller’s ecosystem. And that, frankly, is the most frustrating limit, even if Calibre is for nothing.

Calibre is an excellent all-in-one solution for managing all your e-books.

The Calibre Software is neither the prettiest nor the simplest software. But as soon as you have more than a handful of ebooks, or a reader who refuses your files, it quickly becomes difficult to do without them. For a CDI who manages e-readers or a teacher who distributes texts digitally, it is clearly worth testing.