Website speed and Core Web Vitals: why they’re crucial to your revenue
LCP, INP, CLS: what Google’s Core Web Vitals measure, why a slow website costs you customers and how to improve its performance.
By Léo Chuzel · Published on · 2 min read
A visitor who waits is a visitor who leaves. On mobile, often with an average connection, every second of loading counts. A study published by Google indicates that the probability of a bounce increases by 32% when loading time goes from one to three seconds. For a shop or a practice, that means lost contacts every day.
What are Core Web Vitals?
Core Web Vitals are three metrics defined by Google to measure visitors’ real experience. They’re among the signals taken into account in rankings.
LCP: display speed
Largest Contentful Paint measures the time needed to display the largest visible element of the page, often an image or the main heading. Target: under 2.5 seconds.
INP: responsiveness
Interaction to Next Paint measures the delay between a visitor’s action (a click, typing) and the page’s visible response. Target: under 200 milliseconds.
CLS: visual stability
Cumulative Layout Shift measures unexpected shifts in the layout, such as a button that moves just as you click. Target: a score below 0.1.
How to measure your website’s speed
- PageSpeed Insights: enter your website’s address to get a score and real data from your visitors, if your traffic is sufficient.
- Google Search Console: the “Core Web Vitals” report lists the pages to improve.
- The browser’s developer tools: to analyse precisely what slows a page down.
The most common causes of a slow website
- Heavy images, uncompressed or in outdated formats.
- Too many plugins or scripts: every plugin, chat tool or ad pixel adds weight.
- An overloaded theme that loads code for unused features.
- Low-end hosting or hosting far from your visitors.
- Poorly loaded fonts that delay text display.
- No caching: pages are recomputed on every visit.
How to improve performance
On an existing website, a few actions give quick results: compressing and resizing images, removing unnecessary plugins, deferring non-essential scripts, enabling caching. These optimisations have a limit, however: you can’t turn a heavy theme into a fast website.
To go further, you need to rethink the architecture. Modern technologies like Next.js generate pages in advance or server-side, optimise images automatically and only load the code each page needs. That’s what makes scores above 90 on mobile achievable. For a store, that’s the whole point of a headless Shopify architecture.
Speed, a competitive advantage in Marseille
Many local business websites are built on ageing themes. A website that’s noticeably faster than your competitors’ improves both your rankings and your conversion rate. It’s one of the fundamentals of every one of our website design and redesign projects.