The E-book viewer

calibre includes a built-in E-book viewer that can view all the major e-book formats. The E-book viewer is highly customizable and has many advanced features.

Starting the E-book viewer

You can view any of the books in your calibre library by selecting the book and pressing the View button. This will open up the book in the E-book viewer. You can also launch the E-book viewer by itself from the Start menu in Windows or using the command ebook-viewer in Linux and macOS (you have to install the command line tools on macOS first by going to Preferences → Advanced → Miscellaneous).

Customizing the look and feel of your reading experience

You can change font sizes on the fly by using the font size buttons fontsizei. You can also make the viewer full screen by pressing the Full Screen button fsi. By clicking the Preferences button prefbi, you can change the default fonts used by the viewer to ones you like as well as the default font size when the viewer starts up.

More advanced customization can be achieved by the User stylesheet setting. This is a stylesheet you can set that will be applied to every book. Using it you can do things like have white text on a black background, change paragraph styles, text justification, etc. For examples of custom stylesheets used by calibre’s users, see the forums.

Dictionary lookup

You can look up the meaning of words in the current book by right clicking on a word. calibre uses the publicly available dictionary server at to look up words. The definition is displayed in a small box at the bottom of the screen.

Copying text and images

You can select text and images by dragging the content with your mouse and then right clicking to copy to the clipboard. The copied material can be pasted into another application as plain text and images.