performancecounter - C# Get used memory in %

Question

I've created a performancecounter that can check the total memory usage in %, but the problem is that it doesn't give me the same value as in task manager shows me. for example: my program says 34% but task manager says 40%.

Any ideas?

NOTE
I try to get the available RAM of the system, not the used RAM by a process.

Current Code

private PerformanceCounter performanceCounterRAM = new PerformanceCounter();

performanceCounterRAM.CounterName = "% Committed Bytes In Use";
performanceCounterRAM.CategoryName = "Memory";

progressBarRAM.Value = (int)(performanceCounterRAM.NextValue());
            labelRAM.Text = "RAM: " + progressBarRAM.Value.ToString(CultureInfo.InvariantCulture) + "%";

EDIT
I refresh the progressbar and the label every second with a timer.

Answer 1

You could use GetPerformanceInfo windows API, it shows exactly the same values as Windows Task Manager on Windows 7, here is the console application that get's available physical memory, you could easily get other information that GetPerformanceInfo returns, consult MSDN PERFORMANCE_INFORMATION structure documentation to see how to calculate value in MiB, basically all SIZE_T values are in pages, so you must multiply it with PageSize.

Update: I updated this code to show percentage, it's not optimal because it's calling GetPerformanceInfo two times, but I hope that you get the idea.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace ConsoleApplicationPlayground
{
  class Program
  {
    static void Main(string[] args)
    {
      while (true)
      {
        Int64 phav = PerformanceInfo.GetPhysicalAvailableMemoryInMiB();
        Int64 tot = PerformanceInfo.GetTotalMemoryInMiB();
        decimal percentFree = ((decimal)phav / (decimal)tot) * 100;
        decimal percentOccupied = 100 - percentFree;
        Console.WriteLine("Available Physical Memory (MiB) " + phav.ToString());
        Console.WriteLine("Total Memory (MiB) " + tot.ToString());
        Console.WriteLine("Free (%) " + percentFree.ToString());
        Console.WriteLine("Occupied (%) " + percentOccupied.ToString());
        Console.ReadLine();
      }
    }
  }

  public static class PerformanceInfo
  {
    [DllImport("psapi.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool GetPerformanceInfo([Out] out PerformanceInformation PerformanceInformation, [In] int Size);

    [StructLayout(LayoutKind.Sequential)]
    public struct PerformanceInformation
    {
      public int Size;
      public IntPtr CommitTotal;
      public IntPtr CommitLimit;
      public IntPtr CommitPeak;
      public IntPtr PhysicalTotal;
      public IntPtr PhysicalAvailable;
      public IntPtr SystemCache;
      public IntPtr KernelTotal;
      public IntPtr KernelPaged;
      public IntPtr KernelNonPaged;
      public IntPtr PageSize;
      public int HandlesCount;
      public int ProcessCount;
      public int ThreadCount;
    }

    public static Int64 GetPhysicalAvailableMemoryInMiB()
    {
        PerformanceInformation pi = new PerformanceInformation();
        if (GetPerformanceInfo(out pi, Marshal.SizeOf(pi)))
        {
          return Convert.ToInt64((pi.PhysicalAvailable.ToInt64() * pi.PageSize.ToInt64() / 1048576));
        }
        else
        {
          return -1;
        }

    }

    public static Int64 GetTotalMemoryInMiB()
    {
      PerformanceInformation pi = new PerformanceInformation();
      if (GetPerformanceInfo(out pi, Marshal.SizeOf(pi)))
      {
        return Convert.ToInt64((pi.PhysicalTotal.ToInt64() * pi.PageSize.ToInt64() / 1048576));
      }
      else
      {
        return -1;
      }

    }
  }
}