generic_table_size_calculator.sql

-- from stackoverflow (i miss the author)
SELECT 
    t.NAME AS TableName,    
    p.rows AS RowCounts,
    CONVERT(DECIMAL,SUM(a.total_pages)) * 8 / 1024 / 1024 AS TotalSpaceGB, 
    SUM(a.used_pages)  * 8 / 1024 / 1024 AS UsedSpaceGB , 
    (SUM(a.total_pages) - SUM(a.used_pages)) * 8 / 1024 / 1024 AS UnusedSpaceGB
FROM 
    sys.tables t
INNER JOIN      
    sys.indexes i ON t.OBJECT_ID = i.object_id
INNER JOIN 
    sys.partitions p ON i.object_id = p.OBJECT_ID AND i.index_id = p.index_id
INNER JOIN 
    sys.allocation_units a ON p.partition_id = a.container_id
LEFT OUTER JOIN 
    sys.schemas s ON t.schema_id = s.schema_id
WHERE 
    t.NAME = 'YourTable'
    AND t.is_ms_shipped = 0
    AND i.OBJECT_ID > 255 
GROUP BY 
    t.Name, s.Name, p.Rows
ORDER BY 
    UsedSpaceGB DESC, t.Name