How do I calculate tables size in Oracle

SELECT owner,
       table_name,
       TRUNC(SUM(tb_bytes) / 1024 / 1024) meg,
       TRUNC(SUM(idx_bytes) / 1024 / 1024) idx_meg,
       TRUNC(SUM(lob_bytes) / 1024 / 1024) lob_meg,
       TRUNC(SUM(lob_idx_bytes) / 1024 / 1024) lob_idx_meg
  FROM (SELECT segment_name table_name,
               owner,
               bytes        tb_bytes,
               0            idx_bytes,
               0            lob_bytes,
               0            lob_idx_bytes
          FROM dba_segments
         WHERE segment_type = 'TABLE'
               AND owner IN ('XX', 'APPS', 'GIB')
        UNION ALL
        SELECT i.table_name, i.owner, 0, s.bytes, 0, 0
          FROM dba_indexes i, dba_segments s
         WHERE s.segment_name = i.index_name
               AND s.owner = i.owner
               AND s.segment_type = 'INDEX'
               AND i.owner IN ('XX', 'APPS', 'GIB')
        UNION ALL
        SELECT l.table_name, l.owner, 0, 0, s.bytes, 0
          FROM dba_lobs l, dba_segments s
         WHERE s.segment_name = l.segment_name
               AND s.owner = l.owner
               AND s.segment_type = 'LOBSEGMENT'
               AND l.owner IN ('XX', 'APPS', 'GIB')
        UNION ALL
        SELECT l.table_name, l.owner, 0, 0, 0, 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'
               AND l.owner IN ('XX', 'APPS', 'GIB'))
-- WHERE owner IN upper('&owner')
 GROUP BY table_name, owner
HAVING SUM(tb_bytes) / 1024 / 1024 > 5 /* Ignore really small tables */
 ORDER BY SUM(tb_bytes) DESC;

SELECT owner, table_name, trunc(SUM(tb_bytes) / 1024 / 1024) meg, trunc(SUM(idx_bytes) / 1024 / 1024) idx_meg, trunc(SUM(lob_bytes) / 1024 / 1024) lob_meg, trunc(SUM(lob_idx_bytes) / 1024 / 1024) lob_idx_meg FROM (SELECT segment_name table_name, owner, bytes tb_bytes, 0 idx_bytes, 0 lob_bytes, 0 lob_idx_bytes FROM dba_segments WHERE segment_type = 'TABLE' AND owner IN ('XX', 'APPS', 'GIB') UNION ALL SELECT i.table_name, i.owner, 0, s.bytes, 0, 0 FROM dba_indexes i, dba_segments s WHERE s.segment_name = i.index_name AND s.owner = i.owner AND s.segment_type = 'INDEX' AND i.owner IN ('XX', 'APPS', 'GIB') UNION ALL SELECT l.table_name, l.owner, 0, 0, s.bytes, 0 FROM dba_lobs l, dba_segments s WHERE s.segment_name = l.segment_name AND s.owner = l.owner AND s.segment_type = 'LOBSEGMENT' AND l.owner IN ('XX', 'APPS', 'GIB') UNION ALL SELECT l.table_name, l.owner, 0, 0, 0, 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' AND l.owner IN ('XX', 'APPS', 'GIB')) -- WHERE owner IN upper('&owner') GROUP BY table_name, owner HAVING SUM(tb_bytes) / 1024 / 1024 > 5 /* Ignore really small tables */ ORDER BY SUM(tb_bytes) DESC;