Here’s a TSQL snippet that will give you the sizes of the indexes that the query optimiser isn’t using.  Note that the NULL values are SINCE THE LAST RESTART.  So if you just restarted your server then this is rather a waste of time.

 
SELECT object_name(ui.object_id), si.name as [Index Name],ui.index_id, ui.last_user_seek, ui.last_user_scan, ui.user_seeks, ui.user_scans,
ui.user_lookups,ui.user_updates,
8 * sa.used_pages AS [Index Size]
from sys.dm_db_index_usage_stats ui
inner join sys.indexes si on ui.object_id=si.object_id and ui.index_id=si.index_id
INNER JOIN
sys.partitions sp ON si.object_id = sp.OBJECT_ID AND si.index_id = sp.index_id
INNER JOIN sys.allocation_units AS sa ON sa.container_id = sp.partition_id
where database_id=7
and object_name(ui.object_id) not like ‘sys%’
and ui.last_user_seek is NULL
and ui.last_user_scan is NULL
ORDER by 10 desc