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Lesson 10 Data transfer speed
ObjectiveCalculate data transfer speed.

Data Transfer Speed

When designing a website, it is important for you to consider how much time it takes to download a web page. Both transfer speed and transfer load need to be calculated. This lesson focuses on transfer speed. A separate lesson will cover transfer load.

Estimating Web page transfer speeds

Transfer speed refers to the time it takes to download a Web page. Think about the last time you visited a Web site that tried your patience in terms of waiting time. You probably had a long wait because the files were large and took a long time to download given the speed of your particular Internet connection. When you design Web sites, keep in mind how long it might take a user to download your Web Page. You can use the formula below to help you calculate dowload time:

To calculate Web page transfer speed

  1. Add the size, in bytes, of all the components of the Web page (HTML text, images, video, audio, and JavaScript code, for example).
  2. calculate-web-page-speed. Multiply by 8 to convert bytes to bits.
  3. Divide by the speed of the expected client connection.
For example, a Web page might consist of 2K of HTML text, a 24K corporate logo, and a 4K image file. Adding these components together equals a total page size of 30K. Multiplying 30K by 8 (to convert bytes to bits) equals 240K. If a user were to download this page through a 28.8Kbps modem, dividing 240K by 28.8 reveals that it would take 9 seconds to download this page.
If you want to make your Web site accessible to everyone, it is best to calculate data transfer speed based on the lowest common connection of your assumed audience. If so, assume your users are connecting at 58.6Kbps. (Legacy data rate from the late 1990s)
In the next lesson, you will learn about estimating the server's transfer load.