Page Render Time

Just like page load time, this is a metric of how quickly a web page is loaded, but this measures the time it takes to actually have the web page ready for the visitor to use and interact with. While load time measures the actual time in takes to download images, Js, CSS and other objects in to the visitors browser, render time measure the time it takes to actually process these and show their end-result to the visitor.

Nowadays with heavy use of CSS & JavaScript in web pages, the load time is not always the most accurate metric to determine delay experienced by visitors. Some external content can take many seconds to load even after the actual on-site content of a web page has already loaded.

While not limited to it, client-side A/B or multivariate testing can be one of the legitimate reasons for a longer page render time, as most platforms offering testing such as Google Website Optimizer and Omniture Test & Target employ methods to populate test areas on a web page after it has loaded using JavaScript. This is not exactly a matter of extreme concern, as well-devised tests can contribute to far better conversion than slightly faster rendering time would; and they usually are active for a limited time per section being tested.

Other reasons why the time needed to render a web page for presentation could be longer than the time it takes to download the individual objects that make up the web page are:

  • Processor-intensive demanding code such as compressed JavaScript. While it might be quicker to download a compressed JS file, it may take a visitors computer longer to actually process some such files, adding to the render time.
  • Resource-consuming or large CSS files that could take longer to apply formatting to elements on slower computers.
  • Dependant code that needs third-party code libraries to be loaded before it is run.
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