How to check particular owner size / over all owner size in oracle11g

this is a common question most of the interviewer asked how to find the particular schema/owner size ?
or  how to get the over all schema/owner size in database?


Over all owner size Query

SQL> select OWNER,Segment_type,sum(bytes)/1024/1024/1024 "SIZE_IN_GB" from dba_segments 
 where segment_type='TABLE' group by owner,segment_type order by owner;

Note: if we want to get  particular schema/user  size along   table only (exclude of index,view ) 
use segment_type='TABLE' otherwise just remove this segment_type

Particular schema/owner size  Query

SQL> select OWNER,sum(bytes)/1024/1024/1024 "SIZE_IN_GB" from dba_segments group
 by owner order by owner;