As mentioned by Michael Clark in his post Finder Security Bug or Feature?, the freeware application WhatSize is a quick and easy tool for measuring the size of a given folder and all subfolders and files within it. But WhatSize can only measure based on the permissions of the user who launches it, so you will not be able to measure the size of other user accounts nor folders with special permissions like the root level ‘private’ or ‘.Spotlight-V100’ or other directories inside /System. But here is a way for WhatSize to measure every file on your HD, regardless of permissions:
- Launch Terminal and type sudo followed by a space
- Right-click on the WhatSize application and choose Show Package Contents
- Open the Contents/MacOS folder within to find the WhatSize unix executable file
- Drag that file onto the Terminal window and from within that window, press return
- Enter your administrative password when prompted
The Terminal will fill with some code and WhatSize will now launch, seemingly normally. The difference is that it now has superuser privileges and can read every directory on your hard drive if you ask it to measure. You might be surprised at the difference between folder sizes, especially if you have multiple user accounts on your machine.
But be careful while you’re looking around in this way! Because if you choose a file and hit the Delete button, WhatSize will delete it as the root user and it won’t go in your user account’s Trash to be emptied. I recommend using the Reveal in Finder command and then sending the file to the trash from the Finder, where you’re using your regular user permissions.
Also, don’t close the Terminal window while you’re still running WhatSize, or it will quit WhatSize. Instead, use WhatSize’s File>Quit command, then close the Terminal window.
So if you really, truly want to know exactly what all your space is being used for, run WhatSize with the Terminal’s sudo command.