How to find the size of database?

In general the size of the database is defined as total size of the physical datafiles.

The following query will help you for the space management of your database.

Code:

clear breaks
clear computes
clear columns
set pagesize 50
set linesize 120
set heading on
column tablespace_name heading 'Tablespace' justify left format a20 truncated
column tbsize heading 'Size|(Mb) ' justify left format 9,999,999.99
column tbused heading 'Used|(Mb) ' justify right format 9,999,999.99
column tbfree heading 'Free|(Mb) ' justify right format 9,999,999.99
column tbusedpct heading 'Used % ' justify left format a8
column tbfreepct heading 'Free % ' justify left format a8
break on report
compute sum label 'Totals:' of tbsize tbused tbfree on report
select t.tablespace_name, round(a.bytes,2) tbsize,
nvl(round(c.bytes,2),'0') tbfree,
nvl(round(b.bytes,2),'0') tbused,
to_char(round(100 * (nvl(b.bytes,0)/nvl(a.bytes,1)),2)) || '%' tbusedpct,
to_char(round(100 * (nvl(c.bytes,0)/nvl(a.bytes,1)),2)) || '%' tbfreepct
from dba_tablespaces t,
(select tablespace_name, round(sum(bytes)/1024/1024,2) bytes
from dba_data_files
group by tablespace_name
union
select tablespace_name, round(sum(bytes)/1024/1024,2) bytes
from dba_temp_files
group by tablespace_name ) a,
(select e.tablespace_name, round(sum(e.bytes)/1024/1024,2) bytes
from dba_segments e
group by e.tablespace_name
union
select tablespace_name, sum(max_size) bytes
from v$sort_segment
group by tablespace_name) b,
(select f.tablespace_name, round(sum(f.bytes)/1024/1024,2) bytes
from dba_free_space f
group by f.tablespace_name
union
select tmp.tablespace_name,  (sum(bytes/1024/1024) - sum(max_size)) bytes
from dba_temp_files tmp, v$sort_segment sort
where tmp.tablespace_name = sort.tablespace_name
group by tmp.tablespace_name) c
where
t.tablespace_name = a.tablespace_name (+)
and t.tablespace_name = b.tablespace_name (+)
and t.tablespace_name = c.tablespace_name (+)
order by t.tablespace_name
/

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