Rufnex

FullscreenWidth is a very simple Plugin, that adds a input field to change the editarea width, next to the toolbar buttons at the fullscreen view.
The standard width of the WordPress editarea is 647px, for some reasons this was to small for me. FullscreenWidth let you change the desired width on the fly by simply type widith in the input box. Afer you click elsewhere on the screen the width of the editarea is changed.
Note: The width is set as long you dont reload the browser.

FullscreenWidth

FullscreenWidth adds a input field to change the editarea width, next to the toolbar buttons at the fullscreen view.

scott ogilvie

This plug-in makes your WordPress admin area fixed width instead of the default, elastic. This is perhaps of the most utility to users with larger monitors who enjoy rocking large browser windows, but do not enjoy trying to compose a post in an editor that has line-lengths of more than 200 characters. Why is this not an option in the default WordPress install? We have no fricking idea. But now, at least, there is an easy solution. <a href="http://ogilvi.es/fixed-width-admin/" rel="nofollow ugc">http://ogilvi.es/fixed-width-admin/</a>
<h3>Customization</h3>
You can easily adjust the width of your admin area, its alignment, and the page background color that appears to the left and right of it. Inside the plug-in folder is a file named wp-admin.css, simply open this file in a text editor, and make your changes. All the code has comments that explain the specific functions—don’t be intimidated, just experiment, and if you go too far you can always re-upload the original file.

Fixed Width Admin

Makes the admin area fixed-width instead of elastic. Easy to customize width.

FullscreenWidth vs Fixed Width Admin