Core Web Vitals explained for non-developers
Core Web Vitals are three measures of how a page feels to use. You do not need to be a developer to understand what they are asking.
The short answer
Core Web Vitals measure loading speed (Largest Contentful Paint, LCP), responsiveness (Interaction to Next Paint, INP) and visual stability (Cumulative Layout Shift, CLS). According to Google’s web.dev, “good” means an LCP of 2.5 seconds or less, an INP of 200 milliseconds or less and a CLS of 0.1 or less, measured at the 75th percentile of real visits.
The three metrics
| Metric | What it measures | “Good” threshold |
|---|---|---|
| LCP: Largest Contentful Paint | How quickly the main content (usually a large image or heading) appears | 2.5 seconds or less |
| INP: Interaction to Next Paint | How quickly the page responds when someone taps or clicks | 200 milliseconds or less |
| CLS: Cumulative Layout Shift | How much the page jumps around while loading | 0.1 or less |
LCP: how quickly the main content appears
The usual causes of a slow LCP are a slow server, heavy images, and scripts or styles that block the page from showing. Compressing images, serving them at the right size, and reducing what must load before the first screen all help.
INP: how quickly the page responds
A page feels stuck when heavy scripts keep the browser busy after a tap. Every extra plugin, widget or tracking script adds to the load. Removing what you do not need is often the best fix.
CLS: whether the page jumps around
Layout shift happens when images, ads or fonts load without reserved space and push content down, for example a button that moves just as you tap it. Setting image dimensions and reserving space prevents most of it.
Why they matter to a business
They describe real experience on real devices, which affects how visitors feel about your site and whether they stay to buy or enquire. They are also part of how Google evaluates page experience, as one of many signals; good scores alone do not guarantee rankings. Visitors on phones with slower connections feel poor performance most, which makes it especially relevant for sites with mobile audiences.
How to check your own site
- Open your key pages (home, a service page, checkout) in a testing tool such as PageSpeed Insights.
- Look at the field data (real users) first, and lab data second.
- Note which metric fails, then look at the specific suggestions.
- Test on a phone, not only a computer.
- Re-test after each change.
What to fix first
- Oversized images: resize, compress and use modern formats.
- Too many plugins, apps or tracking scripts.
- Slow hosting or no caching. See web hosting.
- Missing image dimensions that cause layout shift.
- Fonts that load late and shift text.
Our website performance service finds and fixes these, with before-and-after measurements, and the checks belong in a regular routine; see the technical SEO checklist and WordPress maintenance schedule. Store owners should read Shopify vs WooCommerce for how platform choice affects speed.
Frequently asked questions
What is a good Core Web Vitals score?
LCP of 2.5 seconds or less, INP of 200 milliseconds or less and CLS of 0.1 or less, at the 75th percentile of page loads.
Do Core Web Vitals affect rankings?
They are one of many signals about page experience. Relevance and content quality remain more important, so treat speed as part of a good experience, not a ranking trick.
Is INP the same as First Input Delay?
INP replaced First Input Delay as the responsiveness metric. It looks at the responsiveness of interactions across the visit, not only the first.
How often should I test?
After any significant change, and as part of a quarterly review.
Sources and further reading
Facts in this article that come from outside sources are linked here. Everything else is our own recommendation, based on how we build and maintain websites.
- Web Vitals — web.dev — the three metrics and their “good” thresholds
- SEO Starter Guide — Google Search Central — titles, headings, links, sitemaps, content