When a customer sits down to eat at a restaurant, slow service from the waiter often results in poor Yelp reviews and fewer future customers. Similarly, slow site speed can result in poor search engine rankings, lower overall site traffic, and negative user experiences.
Website speed, or website performance, refers to how quickly a browser is able to load fully functional webpages from a given site. Poorly performing sites that render slowly in a browser can drive users away. Conversely, sites that load quickly will typically receive more traffic and have better conversion rates.
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:
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.
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.
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.
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.
Websites that use a CDN (content delivery network) load much more quickly. The Cloudflare CDN caches content in 200 cities around the world in order to store content closer to end users. This reduces latency, because requests from user devices do not have to travel all the way to origin servers, and as a result load time and RTT are much lower.