df -h

This is a good way to find out how many Gigabytes you are using on your drives...

chad@chad-desktop:~/Downloads$ df -h

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       449G  157G  270G  37% /
udev            2.0G  4.0K  2.0G   1% /dev
tmpfs           807M  876K  806M   1% /run
none            5.0M     0  5.0M   0% /run/lock
none            2.0G  2.2M  2.0G   1% /run/shm
/dev/sdf1       466G  369G   98G  80% /media/500G BLUE2
/dev/sdh1       699G  538G  161G  77% /media/Archived STA