Technical Search Engine Optimization: Lazy load images & videos only when needed.

One Technical Search Engine Optimization (Technical SEO) strategy for improving page load time is to lazy load images and lazy load videos only when those resources are required. In this article we’ll take a look at the a3 Lazy Load plugin for WordPress and then review the impact that page load time has in terms of search engines, site visitors, and profit potential — the conclusion follows along with a short quiz.

Introducing the a3 Lazy Load plugin for WordPress

Let’s take a look at one a3 Lazy Load plugin for WordPress (A3LL) . A3LL is not the only plugin that offers delayed loading functionality, however it’s the one I use and we can compare page load performance when the plugin is disabled and then enabled. The A3LL plugin in this example is used to delay the loading of images and videos, specifically, and taking this approach can dramatically shrink the size of a page and improve overall site speed.

Pages that contain videos and images can be potentially very large — if we can delay loading videos and images until they’re actually needed, then the size of the request will drop considerably. Let’s take a look at some test results prior to adding the a3 Lazy Load plugin, below.

WebPagetest performance test results prior to activating the the a3 Lazy Load plugin -- keep an eye on the fully loaded requests, bytes in, and cost.


Performance test results prior to activating the a3 Lazy Load plugin.

In this image we can see that the number of requests is at 102, the fully loaded bytes in is at 2,366KB and the hint that this can be improved is that the cost is high ($$$). If we lazily load the images and videos, this should improve, and this result can be seen in the following image, which includes performance metrics with the a3 Lazy Load plugin enabled.

WebPagetest performance test results after activating the the a3 Lazy Load plugin. Compare this image with the previous one and note that the fully loaded requests, bytes in, and cost are now much lower. This improvement will positively impact the overall site speed.


Performance test results after activating the a3 Lazy Load plugin.

We can see that the number of requests has dropped from 102 to 83 (a 19% improvement), the bytes in has dropped from 2,366KB to 491KB (a 79% improvement), and the cost has dropped from $$$ to $ (an 80% improvement). Overall this is a considerable improvement, one which should help in terms of improving search engine optimization (SEO) for the entire website.

Site Speed as it pertains to Google and Bing

From SEO Best Practices in [1]:

“Google has indicated site speed (and as a result, page speed) is one of the signals used by its algorithm to rank pages. And research has shown that Google might be specifically measuring time to first byte (TTFB) when it considers page speed. In addition, a slow page speed means that search engines can crawl fewer pages using their allocated crawl budget, and this could negatively affect your indexation.” [1]

Note that according to [11], Bing does not consider page load time to be a ranking factor (as of 2020 this may have changed and needs to be reviewed).

Site Speed as it pertains to your visitors

Page speed, or lack thereof, can impact user experience as well. It should be obvious that longer page load times will be directly correlated with a higher bounce rate, less time spent on that page, and lower conversion rates. In “Infographic: Web Performance Impacts Conversion Rates” (#4) we can see just one example of where slow page load time can directly impact the user experience as one in four, or 25% of visitors, will abandon a website which takes more than four seconds to load.

Site Speed as it pertains to your profit

This is even more important if your business makes money online — for example, in [5] we can see that an increase of just one second in page load time could cost Amazon 1.6bn$ in sales over the course of a year.

Another example comes from the article entitled “Impact of slow page load time on website performance” [6] — here we can see that “[f]or every 100 ms of improvement, [Walmart] grew incremental revenue by up to 1%”. Consider that Walmart, including Walmart subsidiaries, was positioned to capture around four percent of online retail spending in the United States by year-end 2018 this equates to around 21bn$ — so that 100ms in page load time is worth substantial money [7].


The links below are worth reading if you’re new to technical SEO and are also interested in the impact that this can have on your bottom line.

If you’re wondering what you should aim for in terms of speed, take a look at the article entitled “How to Find Your Website’s Performance Poverty Line” [8] for a more detailed discussion of this topic. As fast as possible is a simple answer but being able to frame that around some expectations based on visitor data should prove to be helpful. Note that the simple answer may, in fact, be a very expensive answer because at some point delivering further performance improvements becomes difficult to achieve and if the return-on-investment remains mostly unchanged, it’s simply not worth pursuing.

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Lazy Load Quiz

  1. Explain what lazy loading is.
  2. What happens if you’re not lazy loading images, for example, and your page contains many uncompressed images? Assume your website experiences a sudden and unexpected spike in traffic.
  3. Can the Apache modpagespeed module be used to lazily load images?
  4. Name another plugin that delivers lazy loading functionality for WordPress or the content management system you’re using.
  5. If videos are not playing automatically, why would lazy loading them improve page load time and page size?

Related Articles

See Also

  1. Moz Page Speed
  2. How Loading Time Affects Your Bottom Line
  3. Google Speed Update: How Fast Page Speed Should Be For SEO
  4. [Infographic] The Interesting Effect of Speed on Conversion Rates
  5. How Page Load Time Affects Conversion Rates: 12 Case Studies [Infographic]
  6. Impact of slow page load time on website performance
  7. Walmart Passes Apple to become №3 Online Retailer in U.S.
  8. How to Find Your Website’s Performance Poverty Line
  9. SEO Cheat Sheet #2: Page Speed & Image Optimization
  10. Assess Your Website Performance in under Ten Minutes
  11. SEO Beyond Google: How to get 35% more organic traffic from Bing & Yahoo


I am a Technical SEO Consultant and WordPress Specialist based in Northern Virginia. I am interested in software development, content engineering, and business. I'm originally from Chicago, IL, and currently reside in Reston, VA.