How do you get total amount of RAM the computer has?

Using C#, I want to get the total amount of RAM that my computer has. With the PerformanceCounter I can get the amount of Available ram, by setting:

counter.CategoryName = "Memory";
counter.Countername = "Available MBytes";

But I can't seem to find a way to get the total amount of memory. How would I go about doing this?

Update:

MagicKat: I saw that when I was searching, but it doesn't work - "Are you missing an assembly or reference?". I've looked to add that to the References, but I don't see it there.

Add a reference to Microsoft.VisualBasic and a using Microsoft.VisualBasic.Devices;.

The ComputerInfo class has all the information that you need.

Add a reference to Microsoft.VisualBasic.dll, as someone mentioned above. Then getting total physical memory is as simple as this (yes, I tested it):

static ulong GetTotalMemoryInBytes()
{
    return new Microsoft.VisualBasic.Devices.ComputerInfo().TotalPhysicalMemory;
}

The Windows API function GlobalMemoryStatusEx can be called with p/invoke:

  [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
  private class MEMORYSTATUSEX
  {
     public uint dwLength;
     public uint dwMemoryLoad;
     public ulong ullTotalPhys;
     public ulong ullAvailPhys;
     public ulong ullTotalPageFile;
     public ulong ullAvailPageFile;
     public ulong ullTotalVirtual;
     public ulong ullAvailVirtual;
     public ulong ullAvailExtendedVirtual;
     public MEMORYSTATUSEX()
     {
        this.dwLength = (uint)Marshal.SizeOf(typeof(NativeMethods.MEMORYSTATUSEX));
     }
  }


  [return: MarshalAs(UnmanagedType.Bool)]
  [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
  static extern bool GlobalMemoryStatusEx([In, Out] MEMORYSTATUSEX lpBuffer);

Then use like:

ulong installedMemory;
MEMORYSTATUSEX memStatus = new MEMORYSTATUSEX();
if( GlobalMemoryStatusEx( memStatus))
{ 
   installedMemory = memStatus.ullTotalPhys;
}

Or you can use WMI (managed but slower) to query TotalPhysicalMemory in the Win32_ComputerSystem class.

All the answers here, including the accepted one, will give you the total amount of RAM available for use. And that may have been what OP wanted.

But if you are interested in getting the amount of installed RAM, then you'll want to make a call to the GetPhysicallyInstalledSystemMemory function.

From the link, in the Remarks section:

The GetPhysicallyInstalledSystemMemory function retrieves the amount of physically installed RAM from the computer's SMBIOS firmware tables. This can differ from the amount reported by the GlobalMemoryStatusEx function, which sets the ullTotalPhys member of the MEMORYSTATUSEX structure to the amount of physical memory that is available for the operating system to use. The amount of memory available to the operating system can be less than the amount of memory physically installed in the computer because the BIOS and some drivers may reserve memory as I/O regions for memory-mapped devices, making the memory unavailable to the operating system and applications.

Sample code:

[DllImport("kernel32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool GetPhysicallyInstalledSystemMemory(out long TotalMemoryInKilobytes);

static void Main()
{
    long memKb;
    GetPhysicallyInstalledSystemMemory(out memKb);
    Console.WriteLine((memKb / 1024 / 1024) + " GB of RAM installed.");
}