sm$ts_used & sm$ts_free

idle> select * from sm$ts_used;

TABLESPACE_NAME BYTES
------------------------------ ----------
SYSAUX 256573440
UNDOTBS1 8323072
USERS 3211264
SYSTEM 506789888
EXAMPLE 71499776

idle> select * from sm$ts_free;

TABLESPACE_NAME BYTES
------------------------------ ----------
UNDOTBS1 23068672
SYSAUX 15990784
USERS 1966080
SYSTEM 6946816
EXAMPLE 33292288