How to get disk usage from command line?

By using the df command.

Here's an example output:

$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1            303537496  27537816 260580948  10% /
none                    950788       252    950536   1% /dev
none                    959516       232    959284   1% /dev/shm
none                    959516       388    959128   1% /var/run
none                    959516         0    959516   0% /var/lock

Also take a look at its manpage.

ncdu

Works well from the command line. It's ncurses-based and interactive.
You can install it with sudo apt-get install ncdu.

Alternatives

• Top ten: du -shx * | sort -rh | head -10
• If you want more fine grained disk usage, you should take a look at the answers here.