The exact method to calculate your bandwidth....

do these things to calculate.
Create a file of 1mb and upload to your server, and keep a clock (stop watch) ready to count the seconds.
This method will give you the exact speed of your bandwidth.

File size = 1MB
Duration taken to download the file =35secs

Now let us calculate the bandwidth =    1MB      =1024KB
                                                     ____       ______
                                                      35sec      35       

                                       = (29.25 X 8)KB/s = 234Kbps

Your bandwidth is 234Kbps.