The following SQL statement displays all indexes on user tables in the current database, with the related table, whether it’s a clustered index and on which segment it is located:

select so.name as TableName, si.name as IndexName, ss.name as SegmentName, case when (si.status & 16 = 16 OR si.status2 & 512 = 512) then ‘clustered’ else ‘non-clustered’ end as ‘Clustered’ from sysindexes si, syssegments ss, sysobjects so where si.segment=ss.segment and si.id=so.id and so.type=’U’ and si.name != so.name order by so.name, si.name, ss.name

Please note that clustered indexes are usually located on the default segment.

Combine with the output of sp_estspace, you can find out what the required size of the index segment should be.