Tamaño asignado,libre y usado de un tablespace

SELECT 
  a.tablespace_name, 
  b.size_kb/1024 SIZE_MB, 
  (b.size_kb/1024 - a.free_kb/1024 ) USED_MB,
  a.free_kb/1024 FREE_MB,
  Trunc((a.free_kb/b.size_kb) * 100) "FREE_%"
FROM (SELECT tablespace_name, 
   Trunc(Sum(bytes)/1024) free_kb 
FROM dba_free_space 
GROUP BY tablespace_name) a, 
(SELECT tablespace_name, 
  Trunc(Sum(bytes)/1024) size_kb 
FROM dba_data_files 
  GROUP BY tablespace_name) b 
  WHERE a.tablespace_name = b.tablespace_name 
  and a.tablespace_name in ('TABLESPACE1',      'TABLESPACE2') 
 ORDER BY 4 desc;