database size in oracle

To calculate the database size in oracle database use the query below. It actually checks the  database size physical consume on disk.

SQL> select sum(bytes)/1024/1024/1024 size_in_GB from dba_data_files;
 SIZE_IN_GB
----------
4968.95389
 SQL>

And to check the total space used by the data:

SQL> select sum(bytes)/1024/1024/1024 size_in_GB from dba_segments;
 SIZE_IN_GB
----------
4283.73047
 SQL>