Tablespace Size

 SELECT /* + RULE */  df.tablespace_name "Tablespace", 
  df.bytes / (1024 * 1024) "Size (MB)", 
  SUM(fs.bytes) / (1024 * 1024) "Free (MB)", 
  Nvl(Round(SUM(fs.bytes) * 100 / df.bytes),1) "% Free", 
  Round((df.bytes - SUM(fs.bytes)) * 100 / df.bytes) "% Used" 
  FROM dba_free_space fs, 
 (SELECT tablespace_name,SUM(bytes) bytes 
  FROM dba_data_files 
  GROUP BY tablespace_name) df 
WHERE fs.tablespace_name (+)  = df.tablespace_name 
 GROUP BY df.tablespace_name,df.bytes 
UNION ALL 
SELECT /* + RULE */ df.tablespace_name tspace, 
 fs.bytes / (1024 * 1024), 
 SUM(df.bytes_free) / (1024 * 1024), 
 Nvl(Round((SUM(fs.bytes) - df.bytes_used) * 100 / fs.bytes), 1), 
 Round((SUM(fs.bytes) - df.bytes_free) * 100 / fs.bytes) 
  FROM dba_temp_files fs, 
  (SELECT tablespace_name,bytes_free,bytes_used 
    FROM v$temp_space_header 
  GROUP BY tablespace_name,bytes_free,bytes_used) df 
 WHERE fs.tablespace_name (+)  = df.tablespace_name 
 GROUP BY df.tablespace_name,fs.bytes,df.bytes_free,df.bytes_used 
 ORDER BY 4 DESC; 

col SEGMENT_NAME format a20

col SEGMENT_TYPE format a15;

col TABLESPACE_NAME format a25;

SELECT * FROM

(select 

 SEGMENT_NAME, 

 SEGMENT_TYPE, 

 BYTES/1024/1024/1024 GB, 

 TABLESPACE_NAME 

from 

 dba_segments

order by 3 desc ) WHERE

ROWNUM <= 40 AND TABLESPACE_NAME='TABLESPACE_NAME';