Query to Check available Space of an Oracle Database

Login to the database as SYS user

sqlplus as / sysdba

Then copy and paste below sql query in the command line or PL/SQL editor

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;