C#

const long BytesToMBConversion = 1048576;

ManagementObjectSearcher searcher = new ManagementObjectSearcher("SELECT * FROM Win32_PhysicalMemory");
long totalMemSize = 0;

foreach (ManagementObject item in searcher.Get)
{
long currentMemSize = Convert.ToInt64(item("Capacity"));
totalMemSize += currentMemSize;
Console.WriteLine("Memory Size: {0} MB", currentMemSize / BytesToMBConversion);
}

Console.WriteLine("Total memory size: {0} MB", totalMemSize / BytesToMBConversion);

// get physical RAM size (in bytes)
public static long GetPhysicalRAMSize() {
    MEMORYSTATUSEX ms=new MEMORYSTATUSEX();
    ms.Length=64;
    GlobalMemoryStatusEx(ref ms);
    long RAM=ms.TotalPhys;
    RAM=(RAM+0x000FFFFF)&0x7FFFFFFFFFF00000L;   // round up to next 1MB  [EDITED]
    return RAM;
}

[DllImport("kernel32.dll")]
public static extern void GlobalMemoryStatusEx(ref MEMORYSTATUSEX ms);


public struct MEMORYSTATUSEX {
    public int Length;              // DWORD
    public int MemoryLoad;              // DWORD
    public long TotalPhys;              // DWORDLONG
    public long AvailPhys;              // DWORDLONG
    public long TotalPageFile;          // DWORDLONG
    public long AvailPageFile;          // DWORDLONG
    public long TotalVirtual;           // DWORDLONG
    public long AvailVirtual;           // DWORDLONG
    public long AvailExtendedVirtual;       // DWORDLONG
}

Dave Kreskowiak wrote:

Use Win32_PhysicalMemory instead. Add up the Capacity values for all of the PhysicalMemory objects returned and you'll get your total system RAM.