how to get the system dpi settings in c# console application

Try this:

using System;
using System.Runtime.InteropServices;

namespace DPI
{
    class Program
    {
        [DllImport("gdi32.dll")]
        static extern int GetDeviceCaps(IntPtr hdc, int nIndex);

        [DllImport("user32.dll")]
        static extern IntPtr GetDC(IntPtr hWnd);

        /// <summary>
        /// Logical pixels inch in X
        /// </summary>
        const int LOGPIXELSX = 88;
        /// <summary>
        /// Logical pixels inch in Y
        /// </summary>
        const int LOGPIXELSY = 90;

        static void Main(string[] args)
        {
            IntPtr hdc = GetDC(IntPtr.Zero);

            Console.WriteLine(GetDeviceCaps(hdc, LOGPIXELSX));
            // or
            Console.WriteLine(GetDeviceCaps(hdc, LOGPIXELSY));
            Console.ReadKey();
        }
    }
}

No additional references needed. But if it's better to import gdi32 and user32 dll? I dont know - markovl's and Alan N's solutions look more elegant...

The value is stored in the registry

For XP it's at
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\FontDPI LogPixels

You could create a Graphics object from the console window handle:

using (Graphics g = Graphics.FromHwnd(Process.GetCurrentProcess().MainWindowHandle)) {
  Console.WriteLine("X {0:F0}dpi, Y {1:F0}dpi", g.DpiX, g.DpiY);
}

using (RegistryKey key = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\WindowsNT\CurrentVersion\FontDPI")) {
  Console.WriteLine(key.GetValue("LogPixels"));
}

Alan.

A little adaptation

using System;
using System.Drawing;

namespace Helpers
{
    public class DPI
    {
        
        public static float[] GetDpi()
        {
            using (Graphics graphics = Graphics.FromHwnd(IntPtr.Zero))
            {
                float dpiX = graphics.DpiX;
                float dpiY = graphics.DpiY;
                float[] result = new float[] { dpiX = dpiX, dpiY = dpiY };
                return result;
            }
        } 

        
    }
}

using:

float[] Dpi = DPI.GetDpi();
Console.WriteLine(Dpi[0]);

Output: 96