Human Friendly Filesize, from Double Extension Method

Extensions.cs

public static string GetFileSize(this double byteCount)
{
  string size = "0 Bytes";
  if (byteCount >= 1073741824.0)
    size = String.Format("{0:##.##}", byteCount / 1073741824.0) + " GB";
  else if (byteCount >= 1048576.0)
    size = String.Format("{0:##.##}", byteCount / 1048576.0) + " MB";
  else if (byteCount >= 1024.0)
    size = String.Format("{0:##.##}", byteCount / 1024.0) + " KB";
  else if (byteCount > 0 && byteCount < 1024.0)
    size = byteCount.ToString() + " Bytes";

  return size;
}