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.
Te puedes descargar este plugin para utilizarlo en tu instalación autoalojada de WordPress.