Originally Posted by
SpookDroid App file sizes aren't the only thing that makes up an app, though. Temporary downloads, media files (for games, for instance... those don't show as 'media' on your phone, but aren't part of the game install size), etc. OS also takes up space.
I'm accounting for all of those things.
When I look at the space used by a given app, it shows me App size, User data, and Cache. One of the system apps is "Media Storage" and the User data for that app is all the media I have stored (the number exactly matches and changes if I add or remove media). The OS is counting the size of that app (all three parts as I've just described) and is also counting stored media towards the total used storage on the device.