How to find the size of a table in SQL?

SQL Server, nicely formatted table for all tables in KB/MB:

SELECT 
    t.NAME AS TableName,
    s.Name AS SchemaName,
    p.rows AS RowCounts,
    SUM(a.total_pages) * 8 AS TotalSpaceKB, 
    CAST(ROUND(((SUM(a.total_pages) * 8) / 1024.00), 2) AS NUMERIC(36, 2)) AS TotalSpaceMB,
    SUM(a.used_pages) * 8 AS UsedSpaceKB, 
    CAST(ROUND(((SUM(a.used_pages) * 8) / 1024.00), 2) AS NUMERIC(36, 2)) AS UsedSpaceMB, 
    (SUM(a.total_pages) - SUM(a.used_pages)) * 8 AS UnusedSpaceKB,
    CAST(ROUND(((SUM(a.total_pages) - SUM(a.used_pages)) * 8) / 1024.00, 2) AS NUMERIC(36, 2)) AS UnusedSpaceMB
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 NOT LIKE 'dt%' 
    AND t.is_ms_shipped = 0
    AND i.OBJECT_ID > 255 
GROUP BY 
    t.Name, s.Name, p.Rows
ORDER BY 
    t.Name

Here's a simple query, if you are just trying to find the largest tables.

  -- Find largest table partitions
 SELECT top 20 obj.name, LTRIM (STR ( sz.in_row_data_page_count * 8, 15, 0) + ' KB') as Size, * FROM sys.dm_db_partition_stats sz
inner join sys.objects obj on obj.object_id = sz.object_id
  order by sz.in_row_data_page_count desc

In SQL Server run below query you will get table with size of table.

SELECT 
   CASE WHEN (GROUPING(sob.name)=1) THEN 'All_Tables'
   ELSE ISNULL(sob.name, 'unknown') END AS TableName,
   SUM(sys.length) AS ByteLength
FROM sysobjects sob, syscolumns sys
WHERE sob.xtype='u' AND sys.id = sob.id
GROUP BY sob.name
WITH CUBE
ORDER BY SUM(sys.length) DESC