How to find folder/direcotry size – C#

protected override void OnLoad(EventArgs e)
{
    base.OnLoad(e);            
    this.Response.Write(this.FindFolderSize(new DirectoryInfo(Server.MapPath("~"))) + " MB");
}
/// <summary>
/// Find the folder size in MB
/// </summary>
/// <param name="d">Target Direcotry</param>
/// <returns>Folder Size (MB)</returns>
public double FindFolderSize(DirectoryInfo d)
{
    double size = 0;
    foreach (FileInfo f in d.GetFiles())
        size += Convert.ToDouble(f.Length) / (1024 * 1024);
    foreach (DirectoryInfo c in d.GetDirectories())
        size += this.FindFolderSize(c);
    return size;
}