If your disk is mounted at root ("/"), which is the case of most default distro installs, you can run "df -h /" to get only your disk info: user@hostname:~$ df -h / Filesystem Size Used Avail Use% Mounted on /dev/sdc 1007G 49G 908G 6% /
I find it weird that despite having a bunch of options to control output and even filter things, df does not have an option to specify "show me only physical block devices and only once (my /dev/sda4 shows up for various mountpoints but still all show the same size/used/avail values)".