Here is a nice little script I like to use for showing the database size 
for various components.

[code language=”sql”]
#!/bin/ksh ############################################################################
# Script Name..: db_overall_size.ksh
# Description..:
# Author…….:
# Date………: 04/10/2013
# Version……:
# Modified By..:
# Date Modified:
# Comments…..:
# Schema owner.:
# Login User…:
# Run Order….:
# Dependent on.:
# Script type..:
# ############################################################################
sqlplus -s "/ as sysdba" <<EOF
set lines 200
set pages 200
spool db_size.txt set feed off
column systot   format 99,990.99 heading "System |Alloc|GB"
column sysused  format 99,990.99 heading "System |Used|GB"
column systm    format 99,990.99 heading "System Tbsp|MB"
column sysax    format 99,990.99 heading "Sys Aux|GB"
column systmusd format 99,990.99
column sysused  format 99,990.99
column undotb   format 99,990.99 heading "Undo|GB"
column datatot  format 99,990.99 heading "Data|Alloc|GB"
column dataused format 99,990.99 heading "Data|Used|GB"
column tmptot   format 99,990.99 heading "TEMP|Alloc|GB"
column redotot  format 99,990.99 heading "Online|Redo|MB"
column ctltot   format 99,990.99 heading "Ctrl File|MB"
column systall  format 99,990.99 column systused format 99,990.99
column fratot   format 99,990.99 column fraused  format 99,990.99
column total_gb format 99,990.99 column free_gb  format 99,990.99

select name from v\$database;
select s.system_size            SYSTOT,       
s.system_size-f1.free_mb SYSUSED,       
st.system_size           SYSTM,       
sa.system_size           SYSAX,       
ud.system_size           UNDOTB,       
d.data_size              DATATOT,       
d.data_size-f2.free_mb   DATAUSED,       
t.temp_size              TMPTOT,       
r.redo_size              REDOTOT,       
c.controlfile_size       CTLTOT,       
s.system_size+t.temp_size+r.redo_size+c.controlfile_size            SYSTALL,
      s.system_size-f1.free_mb+t.temp_size+r.redo_size+c.controlfile_size SYSTUSED,       
fra.fratot               FRATOT,       
fra.fraused              FRAUSED  
from       (select sum(bytes)/1024/1024/1024 system_size         
from dba_data_files        
where tablespace_name like ‘SYSTEM’ or              
tablespace_name like ‘SYSAUX’ or              
tablespace_name like ‘UNDO%’  or              
tablespace_name like ‘TOOLS’  or              
tablespace_name like ‘USERS’) s,      
(select sum(bytes)/1024/1024/1024 data_size         
from dba_data_files        
where tablespace_name not like ‘SYSTEM’ and              
tablespace_name not like ‘SYSAUX’ and              
tablespace_name not like ‘UNDO%’  and              
tablespace_name not like ‘TOOLS’  and              
tablespace_name not like ‘USERS’) d,      
(select sum(bytes)/1024/1024 system_size         
from dba_data_files        
where tablespace_name like ‘SYSTEM’ ) st,      
(select sum(bytes)/1024/1024/1024 system_size         
from dba_data_files        
where tablespace_name like ‘SYSAUX’ ) sa,      
(select sum(bytes)/1024/1024/1024 system_size         
from dba_data_files        
where tablespace_name like ‘UNDO%’ ) ud,      
(select nvl(sum(bytes),0)/1024/1024/1024 temp_size         
from dba_temp_files) t,      
(select sum(bytes)/1024/1024 redo_size         
from sys.v\$log) r,      
(select sum(BLOCK_SIZE*FILE_SIZE_BLKS)/1024/1024 controlfile_size        
from v\$controlfile) c,      
(select sum(bytes)/1024/1024/1024 FREE_MB         
from dba_free_space        
where tablespace_name like ‘SYSTEM’ or              
tablespace_name like ‘SYSAUX’ and              
tablespace_name like ‘UNDO%’  and              
tablespace_name like ‘TOOLS’  and              
tablespace_name like ‘USERS’) f1,      
(select sum(bytes)/1024/1024/1024 FREE_MB         
from dba_free_space        
where tablespace_name not like ‘SYSTEM’ and              
tablespace_name not like ‘SYSAUX’ and              
tablespace_name not like ‘UNDO%’  and              
tablespace_name not like ‘TOOLS’  and              
tablespace_name not like ‘USERS’) f2,      
(select name, (SPACE_LIMIT)/1024/1024/1024 FRATOT, (space_used)/1024/1024/1024 FRAUSED         
from V\$RECOVERY_FILE_DEST) fra;
spool off
EOF
[/code]