How to Calculate FTP Bandwidth

Calculating your website's available FTP, or file transfer protocol, bandwidth helps you decide if your current bandwidth needs are being addressed. Normally, Web hosts tell you upfront what kind of bandwidth is available, but the number they give you might be misleading. As an example, a Web host might offer "unlimited bandwidth," but that is technically inaccurate, since there is always an upper limit on speed. To illustrate, you might drive on the Autobahn, where this is no speed limit, but you would still be restricted by the capability of your car. To usefully calculate available bandwidth, you need to know the connection speed, rather than a total download limit.

• 1

  Call your Web host and ask what is the FTP connection speed for your website. Usually this number will be in megabits per second, such as 6.0 Mbps. Ask if this figure is shared with other websites, and the peak traffic for those websites. The Web host may also give you two numbers, one for download speed and one for upload speed. Depending on your needs, one might be more important than the other. If you are only interested in the speed at which visitors can download files, the download speed is the one you want.

• 2

  Convert the figure into a more useful figure. Because browsers normally display download speeds as kilobytes per second (KBps), people are more familiar with that measurement. Use the following conversions to calculate the problem:

  1 byte (B) = 8 bits (b)

  1 megabit (Mb) = 1,000 kilobits (Kb)

  1 kilobit (Kb) = 1000 bits (b)

  1 megabyte (MB) = 1024 kilobytes (KB)

  1 kilobyte (KB) = 1,024 bytes (B)

  Using the example 6.0 Mbps, you have to convert this figure to bits first, such that

  6.0 Mb * 1,000 Kb/Mb * 1,000 b/Kb = 6,000,000 bits.

  Convert that figure into bytes, such that:

  6,000,000 bits / 8 b/B = 750,000 bytes

  Convert bytes to kilobytes:

  750,000 B / 1,024 B/KB = 732 KB

  This tells you your maximum connection speed is 732 KB/s, or 732 KBps.

• 3

  Divide this by the number of simultaneous users. If your connection speed is shared with other websites, the number of simultaneous users would also include those of the other websites. As an example, say there are 10 people trying to download a file simultaneously. Use the following formula:

  User download rate = total download rate / number of simultaneous users

  Plugging in the numbers, you would have 732 KBps/10 users, or 73.2 KBps per user. This illustrates the effect multiple users have on the downloading experience of any one user. If you anticipate a lot of simultaneous users, and you wish for them to have fast download speeds, you may consider upgrading your connection speed in this example.