Query to check tablespace size and freespace

 select b.tablespace_name, tbs_size SizeGb, a.free_space FreeGb
 from
 (select tablespace_name, round(sum(bytes)/1024/1024/1024 ,2) as free_space
 from dba_free_space group by tablespace_name) a,
 (select tablespace_name, sum(bytes)/1024/1024/1024 as tbs_size
 from dba_data_files group by tablespace_name
 UNION
 select tablespace_name, sum(bytes)/1024/1024/1024 tbs_size
 from dba_temp_files
 group by tablespace_name ) b
 where a.tablespace_name(+)=b.tablespace_name;