SQL query to find top 50 tables by size

select top50.owner, top50.table_name, meg, a.num_rows
from dba_tables a,
   (Select * from (
SELECT
   owner, table_name, TRUNC(sum(bytes)/1024/1024) Meg
FROM
(SELECT segment_name table_name, owner, bytes
 FROM dba_segments
 WHERE segment_type like 'TABLE%'
 UNION ALL
 SELECT i.table_name, i.owner, s.bytes
 FROM dba_indexes i, dba_segments s
 WHERE s.segment_name = i.index_name
 AND   s.owner = i.owner
 AND   s.segment_type like 'INDEX%'
 UNION ALL
 SELECT l.table_name, l.owner, s.bytes
 FROM dba_lobs l, dba_segments s
 WHERE s.segment_name = l.segment_name
 AND   s.owner = l.owner
 AND   s.segment_type = 'LOBSEGMENT'
 UNION ALL
 SELECT l.table_name, l.owner, s.bytes
 FROM dba_lobs l, dba_segments s
 WHERE s.segment_name = l.index_name
 AND   s.owner = l.owner
 AND   s.segment_type = 'LOBINDEX')
GROUP BY table_name, owner
HAVING SUM(bytes)/1024/1024 > 10  /* Ignore small tables */
ORDER BY SUM(bytes) desc
) where rownum < 51) top50
where top50.owner =a.owner
and top50.table_name = a.table_name
order by meg desc, num_rows desc;


Note: Change 50 to any other number of tables you want to find