Calibre

ApplicationKovid Goyal

Also called calibre ebook, calibre library

Kovid GoyalProductivity

An ebook library and converter. The process is calibre.exe. It is not the Kindle app.

What you need to know

Calibre is a library and converter. Kindle is Amazon's store app.

calibre.exe organizes and converts ebooks you already have. The Kindle for PC app is a different vendor and will not replace this converter.

What is it?: Ebook library
Still current?: Yes, see Current status
Official download?: Use the vendor link in this article

Feex says

If conversion is slow, I would watch calibre-parallel.exe, not the Kindle app. Amazon's client does not do this job.

What is Calibre?

Calibre is an open-source ebook manager. calibre.exe is the library. Conversions can spawn calibre-parallel.exe. The Kindle app will not convert your EPUBs.

If you have never used it

If you need to convert an EPUB, organize a personal ebook library, or talk to a reader over USB, this is Calibre, not the Kindle app. Download it from calibre-ebook.com/download_windows. The Kindle app from Amazon reads Amazon books. Calibre is Kovid Goyal's library and converter. It is not a store.

What is it used for?

Library and metadata

Tag and fetch covers for books you already own. Amazon's Kindle app is a store shelf, not this catalog.

Format conversion

EPUB, AZW3, PDF, and others. That conversion is why people install Calibre next to a Kindle.

Send to device

USB or email-to-device workflows Calibre documents. That is not Amazon's cloud send from the Kindle app alone.

Who is it for?

People who buy EPUBs outside one store
Users who convert before a trip
Anyone who should not open the Kindle app expecting a converter

Current status

Actively developed. 64-bit Windows builds are the current recommendation on the download page.

How old is it?

Kovid Goyal started Calibre in 2006. It is older than many store apps and still GPL. The Kindle for PC app is Amazon's store client. They are not the same library.

Versions

Major channels first. Exact build numbers are not all verified here.

64-bit Windows

Portable

System requirements

Values follow the publisher's public guidance. Workload still changes the real need.

Minimum

Minimum system requirements
Operating system	A current supported Windows 10 or Windows 11 release, per the vendor
RAM	Enough for Windows plus this app. Heavy projects want more.

Resource profile

CPU demand: Follows what you open inside the app
RAM demand: Follows documents, tabs, or libraries

Installed processes

These executables belong to this product when it is installed.

Installed processes
calibre.exe	Library window
calibre-parallel.exe	Worker for conversions

Startup components

Calibre starts when you open the library. The content server is an optional setting, not a Windows service by default.

File locations

Common Calibre locations
Typical install	C:\Program Files\Calibre2\calibre.exe

File formats

EPUBAZW3MOBIPDFCBZ

Common problems

Conversion sits on CPU

Large PDFs to EPUB are heavy. That is expected worker time, not a virus named calibre-parallel.exe.

People look for a Kindle store inside Calibre

Calibre is not Amazon. Buy or sideload the file, then add it here.

Getting unstuck

Install the 64-bit build from calibre-ebook.com/download_windows

A "Calibre ebook crack" search ad is the wrong file.

Do not delete the Calibre library folder while the app is open

The library is your books plus a metadata database. That is not the Kindle documents folder.

If a Kindle book is DRM-locked, Calibre cannot legally strip that

Conversion of files you may convert is the supported story. A "DRM plugin" from a forum is the wrong path.

Alternatives

The Kindle app, Apple Books, and Sumatra PDF overlap for reading. None of them is this converter library.

Official help and downloads

Start with the vendor. Random exe sites are not a support channel.

Official contacts
Download	calibre-ebook.com/download_windows Official installer or vendor page
Help	manual.calibre-ebook.com/ Vendor support
Official site	calibre-ebook.com/download_windows Start here, not a random exe host

Related hardware

Conversions want CPU and disk. An SSD helps large PDF jobs.

Technical details

Vendor version numbers change. This article does not pin a build.

Sources and verification

Reviewed by Feex editorial. Last verified August 2026 Status: Feex Reviewed. How we research.

Calibre official site · Vendor product page
Calibre help · Vendor support
Calibre about · What the project is
Foxhole process map · First-party samples on Windows PCs. Not a lab benchmark.

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