A useful script for checking the size of tablespaces

SET PAGESIZE 100

COL "Tablespace" FOR a22
COL "Used MB" FOR 99,999,999
COL "Free MB" FOR 99,999,999
COL "Total MB" FOR 99,999,999

SELECT df.tablespace_name "Tablespace",
       totalusedspace "Used MB",
       (df.totalspace - tu.totalusedspace) "Free MB",
        df.totalspace "Total MB",
        round(100 * ( (df.totalspace - tu.totalusedspace)/ df.totalspace)) "Pct. Free"
  FROM
    (SELECT tablespace_name,
            round(sum(bytes) / 1048576) TotalSpace
       FROM dba_data_files
       GROUP BY tablespace_name) df,
                (select round(sum(bytes)/(1024*1024)) totalusedspace, tablespace_name
        FROM dba_segments
       GROUP BY tablespace_name) tu
 WHERE df.tablespace_name = tu.tablespace_name
  ORDER BY df.tablespace_name