It's very simple to get the disk size and its utilization in Linux. Just run this command:

df

In return you should see something like that:

user [/home/]# df
Filesystem	1K-blocks	Used	Available	Use%	Mounted on
/dev/sda7	2063504	15775	381136		81%	 /
/dev/sda1	1035660	51652	931400		6% /boot
/dev/sda8	4529120	103776	326129		25%	 /home
/dev/sda6	2063504	58300	1900384	3% /tmp