Get more iPod storage details in iTunes graph
It gives you the details in terms of the iPods storage capacity, that is, in bytes. However, you can also use the graph to display a count of how many songs, photos and videos your iPod contains or how long it would take to listen to all the songs and watch all the videos.
Change to this mode by clicking on the graph itself. Clicking once will cycle to the number count, clicking again will change it to the time count, and clicking one final time will change it back to the storage capacity.