|Tip 84||Calculate All File Sizes|
If you view files and folders in Finder using List view and look under the Size column, you’ll see that although you see the sizes of files, you aren’t told the amount of disk space folders take up. Instead, you see two dashes. To change this, hit Command+J to bring up the View window, and then check Calculate All Sizes. You’ll see the Finder window update instantly, and you can then close the View window.
Note that this is a per-folder setting. To make it a systemwide default, again open the View window, and click the Use as Defaults button.