Jason LeMahieu (MadtownLems)

University of Wisconsin - Cooperative Extension

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.

Media File Sizes

I REALLY needed this, to be able to identify the largest images, and I'm glad to see it still works in April of 2018

Still Works

Easily see how much disk space (in KB, MB, & a percentage of your quota) each of your uploaded files takes up.

Roland Rust

Your webspace is overquota? Your backup files have grown massively? 
Want to know where the really big files are hidden? 
This Plugin is a frontend for the Unix du command.

Disk Usage

Excellent

Displays disk space used by your WordPress website.

Media File Sizes vs Disk Usage