System 7.x

1. Open the hard drive from the desktop, then go under the "View"menu and
    choose "By Icon" (make a note of which one had acheckmark beside it so you
    can set it back to normal when you're finished).
2. Right under the title bar of the hard drive window, it willtell you how much hard disk
    space is used, and how much is left. Restore theprevious settings from the view menu
    and close the hard drive.

System 8.x

1. Click once on the hard drive icon on the desktop to highlightit
2. Go under the File menu and choose "Get Info..."
3. This window will tell you how much hard disk space is used,and how much is left