How to Calculate and Speed-Up the Download Time of Your Web Site
Posted Tuesday, November 30, 2004
Have you ever experienced the frustration of waiting for a web site to download, then giving up and moving on to another? This is because most web users lose their attention after 10 seconds. If your site takes longer than this to load, you will be losing many visitors. This means that the web designer must use images sparingly and choose file formats carefully.
How to Calculate Download Time 1. Check the size of the HTML file and any associated images, files or programs. You can do this by right clicking on the file or image and reading its properties. For example, you may have a page that consists of 10 files, for a total of 84 kilobytes (KB). For a more extensive explanation for calculating file sizes, see my previous article - "How Much Hosting Space Do You Need?" (www.isitebuild.com/hostingspace.htm).
2. Determine the speed of your network connection. Some of the more common speeds are: 14.4 Kbps (kilobits per second) - slow modem speed 28.8 Kbps - typical modem speed for some users. 56 Kbps - typical modem speed for most users with a dial-up connection. 1.544 Mbps (million bits per second) - full T1, enterprise grade network line (equivalent of 24 phone circuits).
3. For this example, we will use 56 kilobits per second (Kbps). The connection speed and file size must be converted to a common unit of measure for division: either bytes or bits. Remember that 1 byte equals 8 bits. The connection speed is already defined in bits: 56 kilobits = 56,000 bits. To convert the file size to bits, you should first convert it to bytes (84 kilobytes = 84,000 bytes). Then convert the bytes to bits by multiplying 84,000 by 8 (1 byte = 8 bits), which results in 672,000 bits.
Divide the file size (672,000 bits) by the connection speed (56,000 bits per second). The bits cancel out, and the results is 12 seconds. This is the amount of time it will theoretically take to download the Web page.
Remember that the figure derived from these four steps, is a theoretical measurement. It does not consider certain factors, such as the fact that 56 Kbps modems rarely operate above 50 Kbps. Nor does it consider network overhead, such as noisy phone lines, or network congestion.
Therefore the best way to determine how quickly users can download your web sites pages, is to test them in a real-world setting. For example, test your web site by accessing it through a dial-up (i.e., telephone) connection. That method will give you a much more reliable estimate.
Factors that Affect the Download Time of Your Site 1. Optimizing Images - this refers to the process of striking a balance between file size and image quality. Your images should not be too large or have too many on your web site. This will cause your pages too long to come up in the users browser and they'll lose their patience.
Of course, if you images are too poor (too small, or with too low of a resolution), your site will be unattractive and it won't matter how quickly the site loads. You need to seek the perfect balance between size and quality.
2. File Formats - There are two main types of images on the Web: GIF (Graphics Interchange Format) and JPEG (Joint Photographic Experts Group) files. Each format compresses files differently and each exhibits different strengths and weaknesses.
The GIF standard works better for images with large areas of similar, flat colors, such as logos, drawings and diagrams.
JPEG is better at compressing photos and images with complex and widely variable colorings. Within each standard, you can adjust quality settings. Those adjustments will affect file size and image appearance.
The key to optimization is to try out all the different options to achieve the smallest possible file size while maintaining an acceptable level of quality.
3. Reuse Your Images - increase the efficiency of your site by making intelligent use of the fact that browsers usually cache (save for later use on the user's hard drive) downloaded files, including Web site images. Therefore, when a page calls for an image that's already been used, it loads and displays much more quickly on subsequent page views because it is coming from a local hard drive rather than the Internet.
Therefore, one of the wisest things you can do is to reuse images; whenever possible, use the same logo on multiple pages, the same graphic buttons and the same graphic dividers. After the first time a user loads these elements, they'll pop up very quickly on subsequent pages.
4. Text - text on pages loads far more quickly than images, permitting you to convey more information more efficiently. Don't have a page on your site that makes the user scroll down several times. Too much text on one page will slow the download time of your site. It will also make it very tiring for your visitor to read all your text.
5. Web Site Enhancements - there are hundreds of other elements you can choose to include on your site. This may include such things as: search boxes, pull down menus, opinion polls, hit counters, rotating banner ads, associate programs etc. You can have a multitude of options to add virtually unlimited functionality (and clutter) to your web site.
To sort out if you need any of these extras, ask yourself the question: How does it help me accomplish the purpose of this web site? If you can't think of a good answer, chances are you don't need the extra element. Make sure they fit into your site's overall aesthetics. Check how they affect load times.
By reducing the download time of your web site, visitors will return because they remembered how fast it was to find what they wanted (rather than the slower site of your competitors). This may ultimately increase the number of your sales.
About the Author
Herman Drost is a Certified Internet Webmaster (CIW) owner and author of iSiteBuild.com Site Design and Low Cost Hosting (http://www.isitebuild.com)