Segue query para validar o tamnho dos objetos dentro de uma determinada tablespace, nesse exemplo estou buscando a tablespace SYSTEM.

SELECT tablespace_name, owner, segment_type "Object Type",
       COUNT(owner) "Number of Objects",
       ROUND(SUM(bytes) / 1024 / 1024, 2) "Total Size in MB"
FROM   sys.dba_segments
WHERE  tablespace_name IN ('SYSTEM')
GROUP BY tablespace_name, owner, segment_type
ORDER BY tablespace_name, owner, segment_type;

TABLESPACE_NAME   OWNER     Object Type        Number of Objects Total Size in MB
----------------- --------- ------------------ ----------------- ----------------
SYSTEM            SYS       TABLE                            548         32154.25

SYSTEM            OUTLN     INDEX                              4              .25
SYSTEM            OUTLN     LOBINDEX                           1              .06
SYSTEM            OUTLN     LOBSEGMENT                         1              .06
SYSTEM            OUTLN     TABLE                              3              .19
SYSTEM            SYS       CLUSTER                            9           129.31
SYSTEM            SYS       INDEX                            650            291.5
SYSTEM            SYS       LOBINDEX                         102             6.44
SYSTEM            SYS       LOBSEGMENT                       102              232
SYSTEM            SYS       NESTED TABLE                      10              .63
SYSTEM            SYS       ROLLBACK                           1              .38

Abs,