Site speed: case studies, tips and tools for improving your conversion rate

There are numerous studies that highlight how important site speed is for the user experience, but in truth it's something that should be obvious to everyone.

Nobody likes to wait ages for web pages to load, particularly when it's so easy to navigate to a competitor's site.

Yet page speed is still an issue for many website owners and they are potentially losing a huge amount of revenue as a result.

To shed more light on how slow site speed might be undermining not only the user experience on your site but also your conversion rates, I've compiled this useful list of case studies, stats, tips and tools...

People expect sites to loads in two seconds

Two studies by Akamai and Gomez are frequently cited in reports into site speed, although both are several years old now so it’s likely that web users’ expectations are even higher now.

The Akamai study, published in September 2009, interviewed 1,048 online shoppers and found that:

  • 47% of people expect a web page to load in two seconds or less.
  • 40% will abandon a web page if it takes more than three seconds to load.
  • 52% of online shoppers claim that quick page loads are important for their loyalty to a site.
  • 14% will start shopping at a different site if page loads are slow, 23% will stop shopping or even walk away from their computer.
  • 64% of shoppers who are dissatisfied with their site visit will go somewhere else to shop next time.

The Gomez report published in 2010, Why Web Performance Matters, interviewed 1,500 consumers about their opinions and website speed. It found that:

  • At peak traffic times, more than 75% of online consumers left for a competitor’s site rather than suffer delays.
  • 88% of online consumers are less likely to return to a site after a bad experience.
  • Almost half expressed a less positive perception of the company overall after a single bad experience.
  • More than a third told others about their disappointing experience.

Slow loading websites cost retailers £1.73bn in lost sales each year

Research published in May by customer data platform QuBit surveyed 60,000 consumers across 80 websites, within a range of industries including retail, travel, technology, finance and publishing.

Using its Exit Feedback tool users were asked to comment on their experience at the point of leaving a website.

Of those surveyed, 8% cited slow loading pages as a key reason for abandoning their purchase. QuBit, which is run by four ex-Googlers, said it is unrealistic to assume all of these users would have completed their purchase. 

Therefore it weighted the average conversion rate of web shoppers (4.35%) against the value of global online sales (£496bn). Based on this estimate, internet retailers could be losing out on £1.73bn each year.

The report also evaluated loading times for pages across a range of industries. It found that on average homepages took 3.50 seconds to load, although some were as slow as 15 seconds.

Product pages were the slowest, taking twice as long to load as homepages across the board.

Site loading times vs. the average

A one second delay in page-load can cause 7% loss in customer conversions

Tag management supplier TagMan ran a test in partnership with glasses e-tailer Glasses Direct to study page speed and conversion behaviour.

It measured the impact of average paid-load time a user experienced to their likelihood to convert on the site and found a significant correlation. The conversion rate peaked at about two seconds, dropping by 6.7% for each additional second.

Furthermore, page-load time for non-converters, users who abandoned the page without converting, was three-to-four times higher than for converters. 

This indicates that visitors who aren’t taking any actions on a site may have abandoned because of the page delays.

Tagman also has a conversion loss calculator so you can work out how much revenue you could gain by speeding up your site.

Site speed for SEO

Not only does slow site speed negatively impact the user experience, but it will also cause your site to be penalised by Google in search results.

For the past two years Google has incorporated site speed as a ranking factor, however it has said that it would impact fewer than 1% of queries and that website owners should still be more concerned with the quality of their sites.

Google’s focus on site speed came after it ran its own usability tests back in 2009.

It found that slowing down the results search page by 100 to 400 miliseconds has a measurable impact on the number of searches per user of -0.2% to -0.6% (averaged over four or six weeks depending on the experiment).

Furthermore, the data showed that users did fewer and fewer searches the longer they were exposed to the experiment.

Users exposed to a 200ms delay since the beginning of the experiment did 0.22% fewer searches during the first three weeks, but 0.36% fewer searches during the second three weeks. 

Similarly, users exposed to a 400ms delay since the beginning of the experiment did 0.44% fewer searches during the first three weeks, but 0.76% fewer searches during the second three weeks.

Even when the page speed returned back to normal it took a long time for people to return to their previous usage level. 

What’s slowing your site down?

We’ve previously blogged about 20 things that could be slowing your site down. Here are a few of the worst offenders:

  1. Ad network code. Ad revenue may be a boon for your bottom line, but ad network code, most of which is JavaScript-based, can make your pages slower.
  2. Analytics tags. Analytics is immensely valuable but JavaScript-based analytics tags can be a detriment to page load times. The good news is that many analytics providers offer asynchronous delivery, but many publishers increase inefficiency by using multiple analytics providers unnecessarily.
  3. Bloated HTML. Bloated HTML not only increases the amount of data that must be transferred to your users, it can have a significant impact on JavaScript performance when you're manipulating the DOM.
  4. Forgetting to Gzip it up. If your server isn't configured to apply Gzip compression to HTML, CSS and JavaScript, you're probably transferring a meaningfully larger amount of data than you have to.
  5. Public networks for private data transfer. One of the first things many publishers do when they need to start to scale is to split their web and database servers. But many don't connect the two using a private network, creating a huge bottleneck and point of failure that can easily impact website performance.
  6. Unoptimized images. On an image-heavy page, a modest 5-10% reduction in file size per image can have a noticeable impact.

The importance of speed for m-commerce

Data included in our Mobile Websites and Apps Optimisation Best Practice Guide reveals just how impatient people are when browsing the mobile web.

Almost three-quarters of respondents (74%) will abandon after waiting five seconds for a mobile site to load, 57% have experienced problems when accessing a mobile site and 46% would not return to a poor performing site.

According to more stats from Gomez, on November 15 last year the average response time for 14 industry-leading mobile retail sites was 4.73 seconds. Amazon led with a response time of 2.85 seconds. 

This is a huge issue, as conversion rate increases 74% when page load time improves from eight to two seconds.

Further stats from the Aberdeen Group show that a one second delay in page load time equals 11% fewer page views, a 16% decrease in customer satisfaction, and 7% loss in conversions.

In real terms, this means that if your site typically earns £10,000 a day, this year you could lose £250,000 in sales.

Tools for testing your site speed

There are a number of different tools you can use to test your site speed, including one from Google.

Here are eight useful examples, courtesy of smashing apps:

Americans are hooked on speed

Data included in an infographic from the Online Graduate Programs shows how important website speed is in the US, with around 25% of people saying they would abandon a webpage that takes more than four seconds to load.

The situation is even more drastic on mobile - 50% of mobile users will abandon a page if it doesn’t load in 10 seconds, and three in five won’t return to that site.

Top 2,000 sites

According to an analysis of the top 2,000 retailers’ websites, the average site now takes 7.12 seconds to load using Internet Explorer 9. In comparison, the average for Chrome is 7.5 seconds and Firefox 7 takes 7.15 seconds.

The strangeloop survey, which is included in this infographic post, found that the top 100 sites tend to be slower than the rest of the top 2,000 and have on average 21 more resource requests.

David Moth is Deputy Editor at Econsultancy. You can follow him on Twitter or connect via Google+ and LinkedIn

Topics: Ecommerce Mobile Customer Experience
Add your own

Reader comments (8)

  1. Mr Marlin Mr Marlin

    SEO at Vacuum tech

    12:01PM on 23rd October 2012

    thanks for tips. now hope for the best response of my site in loading time

  2. Avatar-blank-50x50 Stuart Findlay

    3:33PM on 23rd October 2012

    Great article, with some really good suggestions to improve your page load speed.

    When it comes to customers expectations regarding page load speed, I think it's important to make a distinction between perceived & total page load speed. A page can conceivably take 5+ seconds to load, but if you have content in front of the customer in the first few seconds, and your DOM interaction doesn't interrupt the customers journey, then the customers impression is that the customer can use the site. Deferring the loading of JavaScript or lazy-loading images are a couple of techniques that can help with this.

    There is still the SEO-factor, and I agree that a mobile-optimised site needs to be inherently designed for quick page load speeds. However, if you are looking to increase conversion by having a quicker site, it is still achievable to have a perceived page load speed of 2-3 seconds, whilst having a total page load speed that is a couple of seconds longer.

  3. Avatar-blank-50x50 Louis

    4:41AM on 26th October 2012

    Thanks for this post, David. Great info. I've added this to a roundup of "why speed matters" that I posted a while ago:

    I like these types of posts because this is great info to pass on to clients who might not yet be convinced of the need to pay a developer extra to optimize a website's performance.

  4. Hannah Norman Hannah Norman

    Digital Marketing Executive at Koozai Ltd

    11:52AM on 2nd November 2012

    Really good read. I have just written something similar on the Koozai Blog that complements this one.

    I think site speed is definitely something site owners need to take more notice of these days. Especially now that Google have made a point of commenting on it more regularly!

  5. Deri Jones Deri Jones

    CEO at

    9:31AM on 7th December 2012

    Don't forget - Site speed is not the same as page speed - optimising pages in isolation is good, but it's better to decide on your main money-making User Journeys: and measure them 24/7 so you can optimise them.

    All websites suffer glitches from time to time - Argos were hit this week with issues that caused search journeys to be slow and fail.

    Finding a Product by Search and Adding to Basket: is probably one of the most important Journeys you can optimise!

    Google for: Website wobbles as the snow falls on southern UK

  6. Shoplet Promos Shoplet Promos

    Digital Marketing at Shoplet Promos

    10:11PM on 31st July 2013

    Great stuff. I personally focus on so many different things when working with my clients that page speed is something I forget about. Thanks for this article!

  7. Susie Kinsella Susie Kinsella

    Head of Online Marketing at MonitorHub

    1:47PM on 21st August 2013

    Another tool for getting an overall overview of your website page speed try

  8. Simonne Vickers Simonne Vickers

    Online PR Executive at Summit

    10:16AM on 3rd December 2013

    How to address your site speed:

    -Make site speed a priority amongst your other web pr ojects. Shoppers on mobile devices now make up 30% of r etailers’ site traffic so a fast website is crucial to a good user experience for this audenice.Remember this could be having a direct impact on your conversion rate so it’s important to take action now.

    -Set an acceptable page speed goal for your site - a site that runs faster than three seconds can have a positive impact on site conversion.

    -Run your site through our performance checker not simply at
    regular intervals but at times when results will be most meaningful, for instance across various trading periods

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