
Media File Sizes
by Jason LeMahieu (MadtownLems) on WordPress.org
Easily see how much disk space (in KB, MB, & a percentage of your quota) each of your uploaded files takes up.

A sortable column is added to the Media Library which displays the total space used by this media item (including generated sizes for image files). If a quota is in effect, a color-coded percentage is displayed, based on what percent of the quota this media item is using.
This plugin adds a column to the Media Library page that displays the total space used by each media item. For images, this includes the original image as well as any other generated sizes.
This plugin is particularly handy for networks where site owners have a limited space quota.
Additionally, sorting your Media Library by file size is actually a great way to identify duplicate media items.