First, you will have to figure out what the size of each row is. You can either use a convoluted formula from oracle ( [url]http://technet.oracle.com/docs/products/oracle8i/doc_library/817_doc/server.817/a76956/tables.htm#328[/url] ) or you can insert some sample data, analyze the table, look at the dba_tables.avg_row_len column and multiply by the number of rows you will have.

That being said, you should always allow more room for your tables than you estimate they will take up. If you figure all your data in a year will be 32M, allow for 64M.

Create your data files with the autoextend option on and you will have an easier time of managing your space.