When Google ranks sites in search results, it also takes user experience into account. It uses three main metrics for this, called Core Web Vitals. The technical names sound scary, but the idea is simple: how quickly the site appears, how quickly it responds to a tap, and whether it "jumps around" while loading.
LCP — when does the main content appear?
Largest Contentful Paint is the time it takes for the largest element on the page (usually the main image or heading) to appear on screen. A good result: under 2.5 seconds; over 4 seconds is poor.
How to improve it: upload images in WebP format at the right size (don't send a 3000-pixel image to a phone), choose fast hosting, use a CDN, and take the main image out of "lazy" loading.
INP — how quickly does the site respond to a tap?
Interaction to Next Paint measures how quickly the screen reacts after you press a button or open a menu. It replaced the old FID metric in March 2024. A good result: under 200 milliseconds; over 500 ms is poor.
How to improve it: drop unnecessary JavaScript, heavy plugins and multiple tracking scripts. Every extra chat widget, ad code and social media button weighs on the phone's processor.
CLS — does the page "jump"?
Cumulative Layout Shift measures how much elements move around while the page loads. We all know the situation: you're about to tap a button, an ad loads at the last moment, and you tap something else. A good result: under 0.1; over 0.25 is poor.
How to improve it: set sizes for images and banners in advance, reserve space for elements that load later, and load fonts properly.
Lab data vs real-user data
Measurement tools show two kinds of results. A lab test is a one-off simulation and is good for finding problems. But for rankings, Google looks at the experience of real users over the last 28 days and checks that the result is "good" for 75% of visitors. So getting a "green" result once isn't enough — the site has to open comfortably on a weak phone with a slow connection too.
How do I check?
- PageSpeed Insights — enter your site's address and you'll see results and recommendations for both mobile and desktop. Pay special attention to the mobile result.
- Google Search Console → the "Core Web Vitals" report — real-user data for your whole site, with groups of problem pages.
- The browser itself — in Chrome, press F12 → Lighthouse to test any page.
The most common causes
- Large, unoptimised images and sliders;
- Dozens of plugins and unnecessary scripts loading on every page;
- Weak or overloaded hosting;
- No caching.
If your results aren't good enough, you can hand a technical audit and optimisation of your site to us — we measure first, fix the problem, then measure the result again.
