You can use the following database views to get the information on database size:
i. dba_segments — Gives the information about the used space. You can take a total of all the bytes in the dba_segments view to get the used space.
ii. dba_data__files — Gives the Information on space allocated to datafiles for permanen tablespaces.
iii. v$log— Gives the information on redo log files.
i. dba_segments — Gives the information about the used space. You can take a total of all the bytes in the dba_segments view to get the used space.
ii. dba_data__files — Gives the Information on space allocated to datafiles for permanen tablespaces.
iii. v$log— Gives the information on redo log files.