 <p>I found this to be a little more accurate:</p> <pre><code>SELECT owner, table_name, TRUNC(sum(bytes)/1024/1024/1024) GB FROM (SELECT segment_name table_name, owner, bytes FROM dba_segments WHERE segment_type in ('TABLE','TABLE PARTITION') 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 in ('INDEX','INDEX PARTITION') 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 IN ('LOBSEGMENT','LOB PARTITION') 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') ---WHERE owner in UPPER('&amp;owner') GROUP BY table_name, owner HAVING SUM(bytes)/1024/1024 &gt; 10 /* Ignore really small tables */ ORDER BY SUM(bytes) desc </code></pre>