Speed Test

What does it do?

Measures the use of files on the website, in particular how large they are (and therefore how long they take to load). Also detects some problems which may affect speed, such as missing files.

Why is it important?

Usually the biggest factors in how long a webpage takes to load are:

  1. How large the files used by the website are. Larger files take longer to download.
  2. How many files are required to be downloaded for each page. Each separate file incurs an overhead; even if files are small it can be slow to download many of them in sequence.

Slow pages have been shown to turn visitors away in droves. Conversely, fast pages give visitors a better opinion of your website and encourage them to explore more links.

If a page takes over 8 seconds to display a reasonable portion of content, most people will abandon it entirely. Many users have far lower tolerances than this.

How is it measured?

SiteBeam looks at every file used by every webpage, downloads them and measures their size and type. The score is based on how long the average webpage will take to load in its entirety, for the targeted bandwidth (an option you can set under Site Settings > Test configuration). The ideal loading time - for a perfect score of 10 - is 0.5 seconds. The worst possible loading time is 10 seconds. Pages with a higher importance contribute a greater weight to the overall score.

If the website is missing files, these incur an additional penalty, weighted by the amount of files which are missing per page. Missing files negatively impact performance and may suggest other underlying problems.

Technical explanation

To determine the type of files, SiteBeam uses an intelligent combination of the MIME type reported by the server and the file extension. Where these conflict, SiteBeam logs a warning in the detailed results.

Example conflicts:

  • example.css reports a MIME type text/plain = CSS
  • example.txt reports a MIME type text/html = Text
  • example.mpg reports a MIME type audio/mpeg = MPEG audio
  • example.mpg reports a MIME type video/mpeg = MPEG video

The rules for type deduction are frequently updated.

Each connection speed is weighted down for actual download speed, not theoretical maximum. The default modifier is to use 70% of the theoretical maximum speed for estimates.

Potential problems

File sizes appear too small for some files

This is particularly common with Flash and video files. SiteBeam is reporting the size of the initial file, not the subsequent download which may be initiated by it (for example, the Flash may initiate a pre-loader, which then loads more Flash). There is no way to detect this. SiteBeam is effectively recording the time for the Flash to start.

Some file types not found

If you are using an unrecognised file type (something very obscure), SiteBeam may not recognise it. Alternatively, the webserver may be incorrectly configured and is not explaining what that file type is clearly enough to SiteBeam. Other users may have problems with this file.

How to improve this score

Optimise the website to use smaller files, and less files where possible. Some general advice:

  • Enable GZIP compression for selected formats. For some common file types, a simple technical change to your webserver can significantly improve performance. Compressing some other file types can actually impair overall performance. SiteBeam will suggest which should be modified in the detailed test results.
  • Optimise image formats. Ensure that the correct file format is being used – generally GIF or PNG for images with solid colour, and JPEGs for photos. Ensure appropriate compression keeps the image sizes in check (e.g. reduce the palette, or use more lossy compression for JPEGs). Avoid error diffusion for GIFs unless absolutely essential, as it massively increases file size – PNGs are usually much better.
  • Avoid bloated Javascript. Only include Javascript files that the page actually requires. Most webpages are better served using server-side scripting, which results in much faster pages that are also more likely to be spiderable, accessible and optimised for search engines.

How to use this test effectively

Firstly, always ensure you have set the target Connection speed correctly for your site before using this test. Increasingly, most websites target a medium speed broadband audience, but yours may vary.

Use this test as a health check to see whether your pages are loading quickly enough. Wherever possible, take measures to improve the speed of your website to an appropriate level (this depends on what you have set as the target Internet speed of your audience).

Pay particular attention to this test if your homepage is slow. Ironically despite being the page most sensitive to file size (i.e. users are most likely to leave here) it is also often the largest.

Impact on Summary Scores

Summary Score Percentage Penalty
Accessibility Score 3.8% None
Marketing Score 1.9% None
Overall Score 6.1% Penalty if below 2.2
Technology Score 12.1% Penalty if below 4.4

Further reading