table-and-index-size-in-sql-server
After the script is copied from Rob Garison's answer above
SELECT
i.name AS IndexName,
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')
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
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