Core Web Vitals
Core Web Vitals are Google's three metrics for measuring page experience. They are confirmed ranking factors - Google has stated this explicitly - and they measure what users actually feel when they visit a page: how fast the main content loads, how quickly the page responds to interaction, and how stable the layout is as it loads.
Unlike many SEO signals, Core Web Vitals are measurable, specific, and directly improvable. You can see exactly where your site stands and exactly what is causing problems.
The three metrics
Largest Contentful Paint (LCP) measures how long it takes for the largest visible content element - usually a hero image, video, or large text block - to load. According to Google's own Search Central documentation, a good LCP score is under 2.5 seconds. Between 2.5 and 4 seconds needs improvement. Over 4 seconds is poor.
LCP is the most impactful of the three metrics for SEO and user experience. It is what determines whether a page feels fast or slow. A hero image that takes 3.5 seconds to load will feel slow even if everything else is fast.
Interaction to Next Paint (INP) measures how quickly the page responds visually after a user interaction - a click, tap, or keypress. INP replaced First Input Delay as the interactivity metric. Google's threshold is under 200 milliseconds for a good score. INP catches responsiveness problems that FID missed: a page could have an excellent first-click response time but a slow form submission, and only INP captures both.
Cumulative Layout Shift (CLS) measures visual stability - how much page elements move unexpectedly while loading. A score under 0.1 is good. Common causes are images without explicit width and height attributes, ads that load after content and push the layout, and web fonts that swap in at a different size than the fallback. CLS is the most achievable of the three metrics: according to the Web Almanac's analysis of millions of sites, 81% of mobile pages already achieve a good CLS score.
Why they matter for rankings - and for revenue
Google measures Core Web Vitals at the 75th percentile of real user data - meaning 75% of page loads must meet the thresholds to receive a good rating. According to the Web Almanac, only 48% of mobile pages and 56% of desktop pages pass all three metrics. That means more than half of all sites on mobile are failing Google's page experience standards.
Research from Think with Google found that the probability of a bounce increases by 32% when page load time goes from one second to three seconds. The business consequences compound: an e-commerce platform that improved all three Core Web Vitals thresholds in a documented case study saw an 18% decrease in bounce rate and a 28% increase in organic traffic.
Google has confirmed that Core Web Vitals are a tiebreaker - they do not override content quality and backlinks, but when two pages compete for the same keyword with similar content and authority, the page with better performance scores has the measurable advantage.
How to check your scores
Two tools are standard. Google PageSpeed Insights (pagespeed.web.dev) gives you both lab scores and real-user field data from Google's Chrome User Experience Report. Enter any URL to see LCP, INP, and CLS scores alongside specific recommendations for what is causing problems and how to fix them.
Google Search Console has a dedicated Core Web Vitals report under the Experience section. This shows your site-wide scores across all pages, grouped as Good, Needs Improvement, or Poor. It identifies which specific pages are failing and why, making it the most efficient starting point for prioritising fixes.
The highest-impact improvements
Most LCP problems come from one of four causes: unoptimised images (the most common - see the image optimisation page), slow server response times, render-blocking CSS and JavaScript, and missing preload hints for critical resources. The quickest single win is usually compressing your heaviest images, which my free in-browser image compressor handles without uploading anything.
Most INP problems come from heavy JavaScript that blocks the main thread. The fix is usually deferring non-critical scripts and breaking up long JavaScript tasks.
Most CLS problems come from images without dimensions and dynamically injected content. The fix is straightforward: add explicit width and height attributes to every image, and reserve space for ads and dynamic content before it loads.
Run PageSpeed Insights on your five most important pages - homepage, main service or product pages, and your highest-traffic blog posts. Fix the issues flagged there first. The gains from improving pages that already have traffic are immediate and measurable.