Oracle, table size

The following query (to be run as sys user) is useful to calculate the space used by all tables


SELECT OWNER,
OBJECT_NAME,
OBJECT_TYPE,
TABLESPACE_NAME,
NUM_ROWS,
SUM(KBYTES) KBYTES,
TO_CHAR(DECODE(NUM_ROWS, 0, 0, SUM(KBYTES) / (NUM_ROWS)), '9999.99') KB_ROW
FROM (SELECT LO.OWNER,
LO.TABLE_NAME AS OBJECT_NAME,
EX.SEGMENT_TYPE AS OBJECT_TYPE,
EX.TABLESPACE_NAME,
TS.NUM_ROWS AS NUM_ROWS,
ROUND((SUM(EX.BYTES) / 1024)) AS KBYTES
FROM DBA_EXTENTS EX
JOIN DBA_LOBS LO ON (EX.OWNER = LO.OWNER AND
EX.SEGMENT_NAME = LO.SEGMENT_NAME)
JOIN DBA_TAB_STATISTICS TS ON (LO.OWNER = TS.OWNER AND
LO.TABLE_NAME = TS.TABLE_NAME)
GROUP BY LO.OWNER,
LO.TABLE_NAME,
LO.COLUMN_NAME,
EX.SEGMENT_NAME,
EX.SEGMENT_TYPE,
EX.TABLESPACE_NAME,
TS.NUM_ROWS
UNION ALL
SELECT EX.OWNER,
EX.SEGMENT_NAME AS OBJECT_NAME,
EX.SEGMENT_TYPE AS OBJECT_TYPE,
EX.TABLESPACE_NAME,
TS.NUM_ROWS,
ROUND((SUM(EX.BYTES) / 1024)) AS KBYTES
FROM DBA_EXTENTS EX
LEFT JOIN DBA_LOBS LO ON EX.OWNER = LO.OWNER
AND EX.SEGMENT_NAME = LO.SEGMENT_NAME
JOIN DBA_TAB_STATISTICS TS ON EX.OWNER = TS.OWNER
AND EX.SEGMENT_NAME = TS.TABLE_NAME
GROUP BY EX.OWNER,
EX.SEGMENT_NAME,
EX.SEGMENT_TYPE,
EX.TABLESPACE_NAME,
TS.NUM_ROWS)
WHERE OWNER LIKE 'CF%'
GROUP BY OWNER, OBJECT_NAME, OBJECT_TYPE, TABLESPACE_NAME, NUM_ROWS
ORDER BY KBYTES DESC;