نکته : هر چقدر فایل بزرگتر باشد میزان دقیق تری به دست می آورید .

کد #C :

protected void CheckSpeed(object sender, EventArgs e)
{
    double[] speeds = new double[5];
    for (int i = 0; i < 5; i++)
    {
        int jQueryFileSize = 261; //Size of File in KB.
        WebClient client = new WebClient();
        DateTime startTime = DateTime.Now;
        client.DownloadFile("http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.js", Server.MapPath("~/jQuery.js"));
        DateTime endTime = DateTime.Now;
        speeds[i] = Math.Round((jQueryFileSize / (endTime - startTime).TotalSeconds));
    }
    lblDownloadSpeed.Text = string.Format("Download Speed: {0}KB/s", speeds.Average());
}

Vb.NET :

Protected Sub CheckSpeed(sender As Object, e As EventArgs)
    Dim speeds As Double() = New Double(4) {}
    For i As Integer = 0 To 4
        Dim jQueryFileSize As Integer = 261
        'Size of File in KB.
        Dim client As New WebClient()
        Dim startTime As DateTime = DateTime.Now
        client.DownloadFile("http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.js", Server.MapPath("~/jQuery.js"))
        Dim endTime As DateTime = DateTime.Now
        speeds(i) = Math.Round((jQueryFileSize / (endTime - startTime).TotalSeconds))
    Next
    lblDownloadSpeed.Text = String.Format("Download Speed: {0}KB/s", speeds.Average())
End Sub

در زیر تصویر محاسبه سرعت دانلود را میتوانید مشاهده کنید :