Why is site speed important?
Multiple studies have demonstrated that site speed affects conversion rate (or, the rate at which users complete a desired action). Not only do more users stay on fast-loading sites, they also convert at higher rates compared to slower sites. A number of companies have found that a decrease in page load time of a few milliseconds increases conversions:
Mobify found that decreasing their homepage's load time by 100 milliseconds resulted in a 1.11% uptick in session-based conversion
Retailer AutoAnything experienced a 12-13% increase in sales after cutting page load time in half
Walmart discovered that improving page load time by one second increased conversions by 2%
As a result, improving site performance is a huge part of conversion rate optimization.
The bounce rate is the percentage of users who leave a website after viewing only one page. Users are likely to close the window or click away if a page does not load within a few seconds. BBC discovered that they lost 10% of their total users for every additional second it took for their pages to load.
SEO best practices:
Because Google tends to prioritize getting relevant information to users as quickly as possible, site performance is an important factor in Google search rankings. A site's performance on mobile devices is especially important for SEO.
Long page load times, and poor response times to user actions, create a bad user experience. Waiting for content to load becomes frustrating for users and may provoke them into leaving the site or application altogether.
What factors affect site speed?
Even if a website is designed to be lightweight, it may not load quickly in browsers due to network slowness. The local networking equipment used and the quality of the ISP's services impact network connectivity. Additionally, mobile devices using 3G or 4G instead of connecting to the Internet over WiFi will typically have slower network connections. Although this is largely out of developers' hands, there are still techniques for delivering web resources quickly, even over slow connections. Techniques include minification, compression, and hosting content with a CDN.
If content has to travel a long way to arrive where it is needed, this results in a high amount of network latency. For instance, if a website's HTML and CSS files are hosted in a data center in Ohio, and its images are hosted in a data center in Florida, a user on the west coast will have to wait while all of these files travel thousands of miles to their device.
How can developers measure their website's speed?
A number of companies and organizations offer website speed tests. Many speed tests are able to identify individual elements of a webpage that are slowing the page down, in addition to providing performance metrics.
What website performance metrics are important?
- Load time is how long it takes for an entire webpage to appear in the browser, which means every HTTP request has to be fulfilled. Almost every page on the Internet will require multiple HTTP requests, because multiple resources need to be loaded in addition to the basic HTML of the page.
- Page size is the total file size of all the resources that need to be loaded for the page to function. Page size impacts how long it takes for a browser to load the page, and it can also have a big impact on mobile users, who may be paying for data as they load webpages.
- Time To First Byte (TTFB) measures the amount of time between a browser's request for a webpage and when the very first byte of the response arrives. Overall load time is more important, but TTFB is still taken into account when assessing website performance, and it may impact SEO.
- The number of round trips measures how many times a request/response needs to travel all the way to an origin server and back. The more round trips a webpage requires, the greater the latency.
- Round Trip Time (RTT) is the amount of time it takes for requests to make a round trip, meaning the request reaches the origin server and the response travels back to the device that made the request.