System.Windows.Forms.Screen.PrimaryScreen.Bounds.Size
[DllImport("user32.dll")]
public static extern int EnumDisplaySettings(string deviceName, int modeNum, ref DEVMODE1 devMode);
public struct DEVMODE1 {
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)] public string dmDeviceName;
// детали
DEVMODE1 dm = new DEVMODE1();
User_32.EnumDisplaySettings(null, User_32.ENUM_CURRENT_SETTINGS, ref dm)) ;