Data Conversion

Hello I am a junior dba. I was wondering if anyone could point me how to do the following?: I am currently trying to verify/calculate the size of my current oracle db/schema. I've been using: select sum(bytes)/1024/1024 from dba_data_files + select sum(bytes)/ 1024/1024 from v$log; (NOTE: I ran the two select statements separately. Just thought I'd