DBMS_SPACE.CREATE_INDEX_COST

You can use the procedure dbms_space.create_index_cost to estimate how much space will take place.  In the example below, the used_bytes is how much space is for the index data and the alloc_bytes is how much space is allocated within the tablespace.


SQL> set serverout on
SQL> exec dbms_stats.gather_table_stats('RODBA','EDBA_VMSTATS');

PL/SQL procedure successfully completed.

SQL> variable used_bytes number
SQL> variable alloc_bytes number

SQL> exec dbms_space.create_index_cost('create index RODBA.EDBA_VMSTAT_IX2 on RODBA.EDBA_VMSTATS(runqueue, blocked,cpu_user)',:used_bytes, :alloc_bytes);

PL/SQL procedure successfully completed.

SQL> print :used_bytes

USED_BYTES
----------
    276723

SQL> print :alloc_bytes

ALLOC_BYTES
-----------
     786432