To determine the size of your Oracle database you need to run a few queries and add up the numbers:

sql> select sum(bytes)/1024/1024 from dba_data_files;
sql> select sum(bytes)/1024/1024 from v$log;

Those two queries will tell you how big it is, also if you're in archive log mode, you'll generate files in your archive log destination. Run this query to determine its location:

sql> select * from v$parameter where name = 'log_archive_dest';

If you get something back, you need to add that to the mix as well.