Database server disk size

select round(sum(used.bytes) / 1024 / 1024 / 1024 ) || ' GB' "Database Size",

     round(sum(used.bytes) / 1024 / 1024 / 1024 ) -

     round(free.p / 1024 / 1024 / 1024) || ' GB' "Used space",

     round(free.p / 1024 / 1024 / 1024) || ' GB' "Free space"

from    (select     bytes

     from     v$datafile

     union     all

     select     bytes

     from      v$tempfile

     union      all

     select      bytes

     from      v$log) used

,     (select sum(bytes) as p

     from dba_free_space) free

group by free.p;