Ten things every marketer should know about web performance no. 7: how to find out if a slow mobile site is holding you back

We all know that people use a range of devices to do their online shopping. Some browse on a mobile and buy on a desktop. Others are happier going through the whole process on mobile.

So it’s more important than ever to make sure your site is fast for all of them.

Unfortunately, it’s also harder than ever.

Smartphones and tablets have been around for a while now. And the latest, top of the range phone on a high-speed WiFi network can make your website look blisteringly fast, even if it’s poorly optimised for speed.

But some people have old phones.

Some people don’t have reliable access to 3G, let alone 4G.

Unless you want to exclude these people from your market, you need to make sure your website’s fast enough for them.

Worse still, a good number of these people could be missing from your analytics data. If visitors abandon your site before an analytics tag has had a chance to fire, you’ll never know they were there.

Still, it’s important to use the data you do have to understand the commercial impact of a site that’s too slow on mobile.

For example, a recurring theme for some of our real user monitoring customers is poorer performance on Android smartphones than on iOS. This can have a direct, measurable impact on KPIs such as conversion and bounce rate. 

iOS vs Android performance

Real User Monitoring revealing better performance on iOS for this customer’s site

There are a few reasons for this. One is simply the large range of Android devices. Some will perform well but there is a long tail of lower end devices that will come nowhere near the iPhone in performance terms. You may also find that iPhones are generally faster to process the scripts on your site.

It doesn’t have to be that way.

Yes, the more capable the device, the faster your site will be. But your site doesn’t have to be slow or unusable for people with older, slower smartphones and tablets.

One solution is to detect what kind of device a visitor is using. You can then deliver different content to different types of device. For example, you might decide to avoid using custom fonts on mobile.

This approach has fallen out of favour in recent years, thanks to the rise of responsive design. In a responsive site, page layout reflows to adapt to different viewport sizes, but it’s basically the same content throughout. This is great for creating a consistent look and feel across devices, but it can mask a host of performance problems. Large images designed for desktop screens may just be scaled down to fit mobile viewports instead of being delivered at the most appropriate size. Or scripts that run fast on most devices may be cripplingly slow on others.

If this is happening to you, you’re probably losing customers.

But if you’re going to convince people to put time and resources into making your site faster, you need more to go on.

So the first step is to understand the extent of any problem.

First find out if your site is too slow for certain mobile users.

Then find out how much more you’d be making if your site were faster!

Also in this series:

Ten things every marketer should know about web performance…

1: Why performance matters

2: Big images slow web pages down

3: Traffic affects performance

4: How testing can harm sales

5: Third-party content can slow you down

6: Custom fonts make text slower to display

Published date:  19 October 2017

Written by:  Alex Painter

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