Core Web Vitals – and How to Improve Them

Core Web Vitals are three metrics Google uses to measure how fast, responsive, and visually stable a website is — and they directly affect both where you rank and how many visitors convert. A 0.1-second improvement in mobile load time alone lifted retail conversions by 8.4% in Deloitte and Google’s study of 37 brands (Deloitte/Google, 2020). This guide explains what each metric is, what counts as a “good” score, and the specific changes that improve each one.

Important update: Google replaced the original FID (First Input Delay) metric with INP (Interaction to Next Paint) on 12 March 2024. INP is now the official responsiveness metric inside Core Web Vitals, and this guide uses the current INP thresholds throughout.

Key Takeaways

• Core Web Vitals are three metrics — LCP (loading), INP (responsiveness), CLS (visual stability) — and Google uses them as a ranking signal.
• “Good” thresholds: LCP ≤2.5s, INP ≤200ms, CLS ≤0.1.
• Speed is revenue, not just ranking: a 0.1s faster mobile page lifted conversions 8.4% (Deloitte/Google, 2020), and 40% of users abandon a site that takes over 3 seconds to load.
• Most sites move from Poor to Good with three or four focused changes, starting with images and third-party scripts.

What are Core Web Vitals?

Core Web Vitals are a set of three metrics measuring the experience of loading and interacting with a webpage: loading speed, responsiveness, and visual stability. Google uses them as a confirmed ranking signal alongside mobile-friendliness, HTTPS, and safe browsing, as part of its page experience signals. They sit at the technical heart of any modern build — see our web design and development guide for where performance fits in the wider picture.

Why do Core Web Vitals matter?

They matter because they affect both rankings and revenue at the same time. Some 47% of consumers expect a page to load in two seconds or less, and 40% abandon a site that takes more than three seconds (WP Rocket, 2025). The business case is measurable: in Deloitte and Google’s analysis, a single 0.1-second improvement in mobile load time lifted retail conversions by 8.4%, average order value by 9.2%, and lead-generation form completions by 21.6%.

So the two reasons to care reinforce each other. Sites with good scores rank higher than otherwise-comparable sites with poor scores, and the same speed that wins the ranking keeps visitors from bouncing once they arrive. Improving Core Web Vitals usually lifts conversion rates regardless of the SEO impact.

What are the three Core Web Vitals?

The Core Web Vitals are LCP, INP, and CLS — each rated by Google as Good, Needs Improvement, or Poor against fixed thresholds. The chart below shows where each band begins.

LCP (Largest Contentful Paint)

LCP measures loading performance — the time from page start until the largest visible element (usually the hero image or main heading) finishes rendering. Good is under 2.5 seconds; over 4 seconds is poor.

LCP is most often hurt by large unoptimised hero images, render-blocking JavaScript, slow servers, or unoptimised fonts. Fix one cause at a time and re-measure.

INP (Interaction to Next Paint)

INP measures interactivity — how quickly the page responds when a user clicks, taps, or types. It replaced FID in March 2024 because INP captures responsiveness across the entire visit, not just the first interaction. Good is 200 ms or less.

INP is usually hurt by heavy JavaScript on the main thread, long event handlers, third-party scripts (chat widgets, analytics tags, marketing pixels), and large component trees rendering during interactions. Code-splitting and deferring non-essential scripts are the most common fixes.

CLS (Cumulative Layout Shift)

CLS measures visual stability — how often the layout shifts unexpectedly after the page starts loading. Good is 0.1 or less.

CLS is most often caused by images without width and height attributes, late-loading ads or embeds, web fonts that swap and reflow text, and content injected above existing content. Reserving space for late-loading elements is the single biggest fix.

Which tools measure Core Web Vitals?

Before you can improve them, you need to measure them, and several free tools — most from Google — show your current scores. Use all three: one for quick checks, one for trends, and one for site-wide monitoring.

PageSpeed Insights

PageSpeed Insights gives a quick breakdown of LCP, INP, and CLS for any URL. It separates field data (real-user metrics from Chrome users over the last 28 days) from lab data (a single controlled test). Both matter, but Google uses field data for ranking. Enter your URL, click Analyze, and you get scores plus a prioritised, specific fix list — “Eliminate render-blocking resources”, “Reduce unused JavaScript”, “Image elements do not have explicit width and height” — with the affected files named.

Chrome UX Report (CrUX)

The Chrome User Experience Report is the underlying dataset for the field metrics PageSpeed Insights uses. You can query it directly for time-series data, which is useful for tracking whether your fixes have moved the field-data needle over weeks and months rather than in a single lab test.

Google Search Console Core Web Vitals report

The Core Web Vitals report inside Google Search Console groups your pages by status (Good / Needs Improvement / Poor) and shows exactly which URLs have issues, using real-world field data split by mobile and desktop. For ongoing monitoring it is the most useful of the three — a single place to spot regressions and confirm fixes have rolled out.

How do you improve Core Web Vitals?

For most sites, the largest gains come from doing these five things in order:

1. Optimise images. Use WebP or AVIF, serve appropriately sized images per viewport, and set explicit width and height attributes. This single change usually improves both LCP and CLS.
2. Defer or remove non-essential third-party scripts. Chat widgets, analytics tags, and marketing pixels are the biggest INP killers. Defer them, async-load them, or remove ones you no longer use.
3. Reduce render-blocking CSS and JavaScript. Inline critical CSS for above-the-fold content, defer the rest, and use code splitting on JavaScript.
4. Reserve space for late-loading content. Set explicit dimensions on images, ads, embeds, and iframes, and use font-display: swap with size-adjust fallback metrics to minimise font-swap shift.
5. Choose a faster host or CDN. Hosting matters more than most owners realise — a slow Time to First Byte (TTFB) silently caps how good your LCP can get. This is one reason hosting is a real line item in any WordPress website cost breakdown, not an afterthought.

After every change, re-run PageSpeed Insights and check Search Console field data over the next two to four weeks, since field data updates slowly. For deeper, site-wide speed problems, our guide to website speed optimisation goes further than image tweaks alone.

Why does this matter for SEO?

Because Core Web Vitals directly affect both whether Google surfaces your site and whether visitors stay. If you want to improve your SEO results and reduce bounce rate, they are not optional. The good news is that most sites move from Poor to Good with three or four focused changes — the work is technical but contained, and the impact compounds, because better rankings bring more visitors and a faster experience converts more of them.

For sites with deeper underlying problems, a proper rebuild often pays back faster than incremental tweaks; slow themes, bloated page builders, and unoptimised plugins are common root causes that no amount of image optimisation can fully fix. If a rebuild is on the table, do it carefully — see how to redesign your website without losing SEO first.