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