select name,sum(dbsz)/1024/1024 "Physical siZe MB" from
(select sum(bytes) dbsz from dba_data_files
union all
select sum(bytes) dbsz from dba_temp_files
union all
select sum(bytes) dbsz from v$log),v$database
group by name



OR 


select name,sum(a.dbsz)/1024/1024 "Physical siZe MB",b.actsz/1024/1024 "Actual Size in Mb"
from (select sum(bytes) dbsz from dba_data_files
union all
select sum(bytes) dbsz from dba_temp_files
union all
select sum(bytes) dbsz from v$log) a ,
(select sum(bytes) actsz from dba_extents) b ,v$database
group by name,b.actsz
/


output look like 
NAME      Physical siZe MB Actual Size in Mb
--------- ---------------- -----------------
ARVIND                 6165        2193.00781