How to check database size in Oracle Database?

Below is the script to check the size of the Oracle Database

select (a.data_size+b.temp_size+c.redo_size)/(1024*1024*1024) "total_size GB"
from ( select sum(bytes) data_size
from dba_data_files ) a,
( select nvl(sum(bytes),0) temp_size
from dba_temp_files ) b,
( select sum(bytes) redo_size
from sys.v_$log ) c;