-- from http://social.msdn.microsoft.com/forums/en-US/sqlnetfx/thread/cc1b3e43-0db8-4e75-b5ab-bc2a4c93b12b/
-- MemToLeave values for instance of SQL Server:
-- [Total avail mem, KB] : total memory assigned to MemToLeave
-- [Max free size, KB] : free memory available to MemToLeave
;WITH VAS_Summary AS 
(
	SELECT 
		[Size] = VAS_Dump.Size, 
		Reserved = SUM(CASE(CONVERT(INT, VAS_Dump.Base)^0) WHEN 0 THEN 0 ELSE 1 END), 
		Free = SUM(CASE(CONVERT(INT, VAS_Dump.Base)^0) WHEN 0 THEN 1 ELSE 0 END) 
	FROM 
	( 
		SELECT 
			CONVERT(VARBINARY, SUM(region_size_in_bytes)) [Size], 
			region_allocation_base_address [Base]
		FROM 
			sys.dm_os_virtual_address_dump 
		WHERE 
			region_allocation_base_address <> 0x0 
		GROUP BY 
			region_allocation_base_address 

		UNION 

		SELECT 
			CONVERT(VARBINARY, region_size_in_bytes) [Size], 
			region_allocation_base_address [Base]
		FROM 
			sys.dm_os_virtual_address_dump 
		WHERE 
			region_allocation_base_address = 0x0 
	) AS VAS_Dump 
	GROUP BY [Size]
)
--Get size of all free mem. areas
--http://www.sqlservercentral.com/Forums/Topic624152-386-2.aspx?Update=1
--
SELECT 
	CAST(Size AS BIGINT)/1024 AS [Free size, KB] 
FROM 
	VAS_Summary 
WHERE 
	Free <> 0;