Measuring the Business Impact of Site Speed

Before jumping into the topic, a little bit of background. I'm a techie who has worked on software speed for a decade. Trying to get software to run faster, I have often wondered how fast my site needs to run? Ofcourse, faster the better. But in a constrained world of effort versus gain, is it alright if it loads in five seconds and not three? Or two? What am I leaving on the table by not making it load faster?

Tools like Webpage Test help me test my site on various devices, connections and geolocations. PageSpeed Insights and Browser developer tools let me peek under-the-hood to understand what's causing the slowness. But, how fast does it need to load?

I know a Google study says that "53% of visits are abandoned if a mobile site takes longer than three seconds to load". That is a valuable guideline. But how do I calculate the business impact of site speed for my site from that guideline? Does that 53% abandonment rate apply to my site? How many of my visitors experience my site in three seconds?

Here's how, I think, we can track and analyze speed data for our site to try answer the above questions.

Page Hits and Conversions sliced by their loading speed
Page Visits and Conversions distributed by Page Speed

Now, remember that our site doesn't load up at the same speed for all our visitors due to factors like device, connection type, geolocation and what not. So, if we can slice our conversions by our visitors' speed experience for a given period, we can:

  • Find out the speed that is optimal for our visitors and our conversion rate at that speed
  • Measure the conversions we are losing to visitors who experience our site slower than that optimal speed

Armed with the above numbers, we can say something like this: "If we optimize our site speed to load faster by x seconds for y users, we can potentially gain z conversions". Such a quantification can help us make following data-driven decisions:

  • Prioritize site speed optimization adequately amidst a dozen other conversion optimization tasks
  • Know the target site speed to aim for (based on effort versus gain numbers)

If you can't measure it, you can't improve it.

Ofcourse, we'll then need to analyze what kind of of visitors are experiencing slowness. Why are they experiencing slowness. We'll also need to make sure we track and compare the right speed and conversion metric. But, once we start measuring the loss of revenue due to slowness, we'll start making data-driven decisions towards site speed optimization.