How to determine the Redo Log File size using the Sizing Advice by using the EM Database Control?
Go to the Database Control home page as sysdba; click on the Administration tab; click on the Redo Log Groups link; on this page you can see the redo log group size; select Sizing Advice in the Actions drop-down list and click the Go button. Now, you should see the recommended optimal redo log file size in the Update Message region of the Redo Log Groups page.