sp_spaceused vous donne la taille de tous les index combinés.
Si vous souhaitez connaître la taille de chaque index d'une table, utilisez l'une de ces deux requêtes :
SELECT
i.name AS IndexName,
SUM(s.used_page_count) * 8 AS IndexSizeKB
FROM sys.dm_db_partition_stats AS s
JOIN sys.indexes AS i
ON s.[object_id] = i.[object_id] AND s.index_id = i.index_id
WHERE s.[object_id] = object_id('dbo.TableName')
GROUP BY i.name
ORDER BY i.name
SELECT
i.name AS IndexName,
SUM(page_count * 8) AS IndexSizeKB
FROM sys.dm_db_index_physical_stats(
db_id(), object_id('dbo.TableName'), NULL, NULL, 'DETAILED') AS s
JOIN sys.indexes AS i
ON s.[object_id] = i.[object_id] AND s.index_id = i.index_id
GROUP BY i.name
ORDER BY i.name
Les résultats sont généralement légèrement différents mais à moins de 1 %.