Instructions
Press the gray "Guide" button on your Xbox 360 controller. A menu will appear in the middle of the screen.
Scroll to the far right "System" blade, then open "System Settings."
Choose "Memory." You&'ll then be prompted to make a storage device selection.
Highlight and select your hard drive. This opens a hard drive stored data summary list.
View the hard drive&'s available memory in the upper-right corner of the screen. This does not indicate total hard drive size, only how much memory is available. Notice that there&'s a list of saved data below the available memory number.
View the saved data list below the hard drive&'s available memory number. Add up the memory of each of the nine folders, viewable to the right of each folder, and add that number to the available memory. The sum gives you your hard drive&'s size.