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.
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:
- 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.