The following handy script will show the size of tables, sorted by size.
SELECT schema_name(tab.schema_id) + '.' + tab.name AS [table]
,cast(sum(spc.used_pages * 8) / 1024.00 AS NUMERIC(36, 2)) AS used_mb
,cast(sum(spc.total_pages * 8) / 1024.00 AS NUMERIC(36, 2)) AS allocated_mb
FROM sys.tables tab
INNER JOIN sys.indexes ind ON tab.object_id = ind.object_id
INNER JOIN sys.partitions part ON ind.object_id = part.object_id
AND ind.index_id = part.index_id
INNER JOIN sys.allocation_units spc ON part.partition_id = spc.container_id
GROUP BY schema_name(tab.schema_id) + '.' + tab.name
ORDER BY sum(spc.used_pages) DESC
