How to check tablespace size in oracle database

set linesize 150
set pagesize 5000
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;