SELECT cntr_value / 1024.0 AS TotalServerMemoryMB
FROM   sys.dm_os_performance_counters
WHERE  counter_name = 'Total Server Memory (KB)';

SELECT  CAST(physical_memory_in_bytes / (1024.0 * 1024.0 * 1024.0) AS DECIMAL(20, 2)) AS PhysicalMemoryGB,
        CAST((bpool_committed * 8) / (1024.0 * 1024.0) AS DECIMAL(20, 2)) AS BufferPoolCommittedMemoryGB
FROM    sys.dm_os_sys_info;