How to check schema size in oracle database

Below script to know the schema size in oracle database.

Script:

set linesize 160
set pagesize 10000
col owner for a15
col segment_name for a30
col segment_type for a20
col TABLESPACE_NAME for a30
clear breaks
clear computes
compute sum of SIZE_IN_GB on report
break on report
select OWNER,sum(bytes)/1024/1024/1000 "SIZE_IN_GB" from dba_segments group by owner order by owner;