CKSource

To define the default size of the editor, use the width and height configuration settings.

Note that the width value can be given as a number representing the value in pixels or as a percent representing the size relative to the parent element containing the editor.

config.width = 850;
config.width = '75%';

The height value defines the height of CKEditor editing area and can be given in pixels or em. Percent values are not supported.

config.height = 500;
config.height = '25em';
config.height = '300px';