When a page is slow to load, people don’t wait: they go back and click the next result. Google measures that behaviour, and also uses speed directly as a ranking factor through the Core Web Vitals.
Put differently: a slow site costs you twice. You lose whoever already arrived, and you rank worse for whoever hasn’t yet.
The three Core Web Vitals, in plain terms
LCP — how long until the important part appears
Measures the time until the largest element on screen paints, usually the main image or headline. It’s the metric that best reflects the feeling of "this has loaded".
INP — how long until it responds to a tap
Measures the delay between a user pressing something and the page reacting. A site can look fast and feel slow if JavaScript has it blocked.
CLS — how much the content jumps while loading
Measures layout shift: that moment when you go to press a button, a late image loads and the button moves. The metric that irritates users most and the easiest to fix.
How to measure it without fooling yourself
- PageSpeed Insights: gives lab data and, if your site has enough traffic, real-user data. The latter is what counts.
- Search Console: the Core Web Vitals section tells you which URLs genuinely fail for your visitors, grouped by problem type.
- Always test on mobile and on a throttled connection. Measuring on your fibre-connected desktop tells you nothing useful.
One warning: the 0–100 score is indicative, not a target. Chasing 100 on a real online store burns hours. What matters is passing all three metrics for real users.
The five causes behind almost every slow site
- Unoptimised images. Uploading the 4 MB photo straight from the camera is, by a distance, problem number one.
- Too many plugins or apps. Each adds its CSS and JavaScript, and many load on every page though they’re used on one.
- Undersized hosting. Three-euro shared hosting works until you have real traffic.
- Third-party fonts and scripts. Every chat widget, map, pixel and embed is another request to a server you don’t control.
- No caching. Rebuilding the same page from scratch on every visit is repeated work you can avoid.
Where to start if your site is slow
In this order, because it delivers the most per hour invested: compress and resize images, enable caching, remove unused plugins — and only then consider changing hosting or rebuilding anything.
And measure before and after. Without the baseline you won’t know what worked, and you’ll keep repeating things that don’t help because they "seemed" to.
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