DB Admin

Hi..,
How can I find the Size of my Database..?
Through OEM it is saying that
Database Size (GB) 22.609 (Home-->Space Summary-->Database Size (GB))

But if I give the following command it is giving the out put as 17.96 GB , why this much of difference, can u pl. explain..?

select ((sum(bytes)/1024)/1024)/1024 from dba_data_files


Thanks in Advance
Giri K.Y.

10g?... you are missing dba_temp_files.

and redo log files and control files