Why Are WordPress Sites Slow? Diving into our CMS Benchmark
In an earlier blog post, we analyzed the performance of sites on 8 major CMS platforms. In the process, we ran tests on nearly 15,000 sites — and with that data on hand, we’d be remiss not to dig a little deeper. Mostly, we sought to gain some additional insight into why WordPress scored worst in our benchmark — and what we’ve found seems to support our hypothesis.
Overall Performance – The Full Field
In our first post, we looked at median figures of Time to Interact for thousands of sites across 8 CMS platforms. But how was that performance distributed? This histogram shows Time to Interact across all of the sites studied. (The median Time to Interact for the full set was 7,088 – just a tad over 7 seconds).
- When we spread performance across bins of 500 milliseconds, we saw that the highest frequencies were just below the median, and those after the median were spread across a long, even rundown.
- It seems that the 4.5 second threshold is hard to break. Less than 600 sites fall into the “”4000 – 4500″” bin, while about 1000 fall into the “”4500 – 1000″” bin. That’s the largest gap between two sequential bins.
- A prevailing idea in WPO is that a 2 second load time is a benchmark of fantastic performance. The above data shows a pitiful number of sites are even in the ballpark: only 2.2% of the sites studied clocked in at less than 3 seconds.
Histograms by CMS (WordPress and Drupal)
Our last post generated a lot of questions about WordPress — not surprising since it’s the most popular platform by far, as well as the worst performer. For the chart above, we did another histogram of TTI, but this time compared data from Drupal and WordPress. (We chose Drupal for this comparison because its median performance was closest to the overall median of 7 seconds).
We see that Drupal’s performance distribution looks similar to the overall Time to Interact distribution from the first chart, with highest frequencies around 5 to 6 seconds, and smooth, steady drop off in frequency as performance gets worse. Conversely, WordPress sites see steady frequencies from 6 to 10 seconds, and show more sites per bin than Drupal as performance gets worse (plus a good amount “”more”” than 20 seconds).
JS weight was not the highest-correlating factor with Time to Interact — overall asset count, asset weight, number of domains, and number of images had higher coefficients. But when it’s graphed, it’s clear that there is a demonstrable link.
Why WordPress is Slow