Verificar o tamanho do DB

Esta consulta tras o tamnho do DB, esparço usado e livre.

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