TheMusicPirate,
are those the sizes of all your directories? In that case you can simply go to your DOS prompt (Start > Run > cmd.exe) and enter and execute the following dos command:
DIR c:\ /S
this will start to list everything on your disk and at the end will show you how much bytes it is in total.
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Or, of course, you could always right click the drive in Windows Explorer and look at the amount of bytes used.