Mobile optimisation for e-commerce: speed, UX and checkout for your webshop

Your webshop can look perfect on your laptop and still lose customers every day, because most of your visitors see it on a fifteen-centimetre phone screen, often on a shaky 4G connection. Mobile optimisation is therefore not a finishing touch but the core of e-commerce optimisation: Google now indexes only your mobile version, and it is precisely on mobile that buyers drop out most often. In this guide you get a concrete action plan: what mobile optimisation involves, why mobile converts worse, how to make your webshop faster, which Core Web Vitals thresholds to hit and how to make your checkout mobile-proof. Platform-neutral, with the official Google thresholds and current research figures. At ClickForest we build and optimise webshops for SMEs in Flanders, so everything below comes straight from that practice.

What is mobile optimisation for a webshop?

Mobile optimisation is the set of adjustments that makes your webshop fast, usable and buyable on a smartphone: load time, layout, one-thumb operation, readability without zooming and a checkout with mobile payment methods. It goes beyond a responsive theme; the fact that your site scales with the screen does not mean it works pleasantly there.

In practice the work falls into four layers. Speed: how quickly the page becomes usable on screen, even on a mediocre mobile connection. UX: can you navigate, search and filter with one thumb, without mis-taps or intrusive pop-ups. Content: are product photos, texts and buttons made for a small screen. And the checkout: can you pay without endless typing. Each layer has its own quick wins, and together they determine your mobile conversion rate. The rest of this article walks through them step by step.

Why is mobile optimisation so important for e-commerce?

Two reasons: your visitors and Google. Worldwide, 69.9 percent of all web traffic comes via mobile (Contentsquare, 2026, all sectors), and since July 2024 Google crawls and indexes exclusively with its smartphone crawler. A webshop that does not work on mobile is literally no longer indexable for Google and frustrating for most visitors.

That indexing switch has been flipped for good: mobile-first indexing was completed at the end of October 2023, and since 5 July 2024 there is no longer even a desktop-crawler exception. In Google’s own words: “If your site’s content is not accessible at all with a mobile device, it will no longer be indexable.” Your mobile version is your site, including for your SEO rankings. For Belgium an honest nuance applies: measured across all web traffic, desktop still leads here by a small margin (53.56 percent versus 44.17 percent mobile and 2.27 percent tablet, Statcounter, June 2026). But anyone who opens their own analytics sees big differences per audience and per moment, and the trend points the same way everywhere: desktop traffic fell 7.3 percent year on year worldwide. How the broader Belgian market is evolving is covered in our analysis of the e-commerce trends in Belgium.

Why does mobile convert worse than desktop?

Because buying on a small screen creates more friction: slower loading, smaller tap targets, more typing and more distraction. According to Contentsquare (2026), desktop converts 74 percent higher than mobile, and mobile shopping carts are abandoned roughly ten percentage points more often than desktop carts (Dynamic Yield benchmark, June 2026). That gap is partly behaviour, but mostly friction you can remove.

The behavioural part first: mobile visitors browse more, compare on the sofa and sometimes check out later on desktop; the average across all studies is high anyway, at 70.22 percent abandoned carts (Baymard, meta-average of 50 studies). But the friction is the lever. In its 2025 benchmark, Baymard found that 63 percent of mobile sites score “mediocre” or worse on checkout UX; the majority of webshops therefore have something to gain. How big that gain can be is summed up by Baymard researcher Kathryn Reeves:

“Baymard’s research findings further reveal that the average large-sized ecommerce site can gain as much as a 35% increase in conversion rate just by making design changes to their checkout process.”

— Kathryn Reeves, Senior UX Researcher at Baymard Institute

That figure is about large sites, not an SME promise, but the direction applies to everyone: the mobile conversion gap is not a law of nature. Where exactly to look when your webshop underperforms is covered in our diagnostic guide why is my webshop not converting?; the systematic approach is in conversion optimisation for e-commerce.

How do you make your webshop faster on mobile?

Tackle the three biggest slowdowns: superfluous scripts and apps, images that are too heavy and a slow theme. On mobile, speed is the foundation under everything else, and the gain is measurable: in the Deloitte study Milliseconds Make Millions (2020, with Google), 0.1 seconds of speed gain on mobile correlated with clearly better retail figures.

“Retail conversions increased by 8.4% and average order value increased by 9.2%.”

— Deloitte, in the research report “Milliseconds Make Millions” (2020, 37 European and American brand sites)

It is a correlation study and six years old by now, so read it as direction, not as a guarantee. It does still set the order of work:

1. Clean up scripts and apps. Every tracking pixel, review widget and pop-up app loads on every page. Remove what you do not demonstrably use; with existing webshops this is almost always the biggest win.
2. Optimise images. A modern format (WebP or AVIF), the right dimensions per screen, lazy loading below the fold and correct prioritisation of the hero image.
3. Choose or keep a light theme. A heavy theme with dozens of features you never use is dragged along on every page. For a new shop this is the easiest choice to make upfront; how to make it is covered in our step-by-step guide to setting up a Shopify webshop.
4. Avoid layout shifts. Reserve space for images, banners and embeds so the page does not jump around while loading; that is also your CLS score (more on that below).

Measure before and after every intervention with PageSpeed Insights, otherwise you are optimising on gut feeling.

What are Core Web Vitals and which values should you hit?

Core Web Vitals are the three measurements Google uses to judge the user experience of your pages: loading speed (LCP), responsiveness (INP) and visual stability (CLS). The official thresholds: LCP within 2.5 seconds, INP at most 200 milliseconds and CLS at most 0.1, each measured at the 75th percentile of your real visitors.

Metric	What it measures	Good score (web.dev)
LCP (Largest Contentful Paint)	How quickly the largest element (usually your product photo) is visible	Within 2.5 seconds
INP (Interaction to Next Paint)	How quickly the page responds to taps and typing	At most 200 milliseconds
CLS (Cumulative Layout Shift)	How much the layout shifts while loading	At most 0.1

INP is the youngest of the three: on 12 March 2024 it replaced the older FID metric, and it is stricter because it measures all interactions instead of only the first. Google itself sums up the design like this:

“Each of the Core Web Vitals represents a distinct facet of the user experience, is measurable in the field, and reflects the real-world experience of a critical user-centric outcome.”

— Google, in the official web.dev documentation on Web Vitals

That “in the field” is the most important phrase: the thresholds apply to real visitor data (field data from the Chrome UX Report), not to the lab score a tool calculates on your desktop. A webshop that turns green in a lab test but sits in the red for real mobile visitors on 4G simply fails.

How do you optimise the checkout for mobile?

Less typing, fewer steps, more mobile payment methods. In 2024 the average checkout still counted 11.3 form fields while 8 suffice (Baymard); on a phone keyboard every unnecessary field feels twice as heavy. Offer guest checkout, show all costs upfront and let people pay with one thumb via Bancontact Pay, Apple Pay or Google Pay.

For a webshop in Flanders that payment step is no detail. Bancontact is the standard here, and payment behaviour is already massively mobile: in 2025 Bancontact counted 526 million mobile payments (up 11.6 percent year on year) and 48 percent of Belgians paid via QR code, according to the company itself. Since March 2026 the app is officially called Bancontact Pay (formerly Payconiq by Bancontact); name it that way on your payment page. Beyond that the classics apply, all straight from checkout research: autocomplete on address fields, the right keyboard per field type (numbers for a card number), error messages next to the field instead of at the top, and no mandatory account registration. Want to dig deeper, then conversion optimisation for e-commerce is the follow-up article; ClickForest carries out these checkout optimisations within CRO programmes for SMEs in Flanders.

Wondering where your webshop is leaving mobile points on the table? ClickForest walks through the entire mobile funnel with SMEs in Flanders, from load time to checkout, within Shopify e-commerce guidance or a CRO programme. Book a no-obligation video call.

How do you test whether your webshop is mobile-friendly?

With three free instruments side by side: PageSpeed Insights (field data and lab score per URL), the Core Web Vitals report in Google Search Console (problems grouped across your whole shop) and your own phone, on which you place a complete order yourself every month. Each test catches problems the other two miss.

The order that works in practice: start in Search Console, because there you see at a glance which page groups (product pages, collections, blog) sink below the thresholds for real visitors. Then analyse one representative URL per group in PageSpeed Insights and follow the concrete recommendations. And finish on a real device, preferably a mid-range phone a few years old on a mobile network instead of your fast wifi: search for a product, filter, add to cart and check out up to and including the payment step. That last test takes ten minutes and invariably finds the friction no tool reports, from a cookie banner covering the buy button to a discount field that makes the keyboard flip.

Responsive or mobile first: what is the difference?

Responsive design means one website adapts to every screen size; mobile first is the design order in which you start from the smallest screen and only then expand to desktop. They are not competitors: a modern webshop is built responsive and designed mobile first. The order determines the quality of the choices.

The term comes from Luke Wroblewski’s essay of the same name from 2009, and his core argument is more relevant today than it was then:

“Mobile devices require software development teams to focus on only the most important data and actions in an application. There simply isn’t room in a 320 by 480 pixel screen for extraneous, unnecessary elements. You have to prioritize.”

— Luke Wroblewski, author of “Mobile First”, in his original 2009 essay

Design for desktop first and then “shrink”, and you end up with a mobile site full of compromises: menus with too many levels, tables that do not fit, texts nobody reads on a phone. Start mobile and you force yourself to choose what really matters, and that sharper story then turns out to work better on desktop too. If you are having a new site or webshop built, make that order an explicit part of the briefing; it is one of the points we at ClickForest lock in as standard for website development for SMEs in Flanders.

What should you remember about mobile optimisation?

Mobile optimisation is the basis of modern e-commerce optimisation, not a nice-to-have: Google only indexes your mobile version and most traffic is mobile. The action plan: make your shop fast (scripts, images, theme), hit the Core Web Vitals thresholds for real visitors, design mobile first and strip the checkout down to fewer fields with mobile payment methods such as Bancontact Pay. Test with PageSpeed Insights, Search Console and your phone.

ClickForest helps SMEs in Flanders build fast, mobile-converting webshops: from Shopify guidance and maintenance to CRO programmes. Curious where your shop is falling short on mobile? Book a no-obligation video call and we will look at your numbers together.