--- title: Core Web Vitals — definition and what they measure | Siite description: "Core Web Vitals explained: what LCP, INP and CLS measure, how field data differs from lab scores, and why speed matters most on mobile landing pages." url: "https://siite.co/dictionary/core-web-vitals" type: static generatedAt: "2026-10-22T08:21:10.756Z" --- Web & Technical # Core Web Vitals Google's three field metrics for page experience — Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift — measured from real visitors. Also goes by CWV, LCP, INP, CLS [![Siite](/images/layout/logo.svg)Written by Siite](/about/)Updated September 8, 2026 ## Entry contents [All Terms A to Z←Browse the full dictionary](/dictionary/) Core Web Vitals are three metrics Google uses to describe page experience, all measured from real visitors rather than from a test. They are the closest thing to an objective answer to whether a page feels fast, and they tend to be worst exactly where it matters most: on a phone, on a weak connection, on the page somebody landed on in a hurry. > **Briefly explained** > > - Three metrics: LCP, INP and CLS. > - The figures come from people who actually visited, not from a simulation. > - A tiebreaker for ranking, and a real factor in conversion. > - Usually broken by images, scripts and hosting. ## What do the three measure? - **Largest Contentful Paint (LCP):** How long until the main content is visible. The headline number. - **Interaction to Next Paint (INP):** The delay between a tap and the page doing something about it. - **Cumulative Layout Shift (CLS):** Whether things move under the reader’s thumb as the page assembles. The reason people tap the wrong button. ## Why does lab data disagree with the report? Because they measure different things. A speed test runs once, on a simulated device, in good conditions. Search Console reports what actually happened to real visitors over the past 28 days, on whatever phones and connections they had. A perfect lab score sitting next to failing field data is normal. Trust the field data, and expect weeks rather than days before a fix shows up in it. ## Why does it matter beyond ranking? The damage is done before ranking becomes relevant at all. Most urgent searches happen on a phone, often on a poor connection. A page that takes several seconds to show a phone number loses the caller outright. And in paid search, page experience feeds [Quality Score](/dictionary/quality-score/), so a slow page raises what you pay for the click as well as wasting it. ## What usually causes failures? - Uncompressed hero images and background video - Chat widgets, tracking tags and review badges loading before the content - Fonts that swap in late and shift everything down the page - Shared hosting with a slow server response The fix is rarely one setting. It is image discipline, restraint with third-party scripts, and [hosting](/dictionary/hosting/) that answers quickly. ## What do the terms mean? - **Field data:** Measurements from real visitors. What Google uses. - **Lab data:** A simulated test. Useful for debugging, not for judging. - **LCP:** Time until the main content appears. - **INP:** Responsiveness to taps and clicks. - **CLS:** How much the layout moves while loading. Owner questions ## What owners ask us about Core Web Vitals ### My speed test passes and Search Console fails. Which one is right? +Because a test is a lab measurement on a simulated device, and Search Console reports field data from real visitors on real connections. The field data is what counts. ### Are they a ranking factor? +They are part of page experience, which Google treats as closer to a tiebreaker than a primary signal. The larger effect is on conversion: a slow page loses the caller before ranking matters. ### What usually breaks them? +Oversized hero images, chat widgets and tracking tags loading ahead of the content, fonts that swap late, and slow hosting. ### How long before a fix shows up? +Field data is reported on a rolling 28-day window, so expect weeks rather than days before the report reflects what you changed. ### Which page should I fix first? +The one your ads point at. You are paying for those visits, and a slow landing page costs you twice: in lost calls and in a higher click price.Put this to work ## Guides that use this Step-by-step playbooks from the team, written for owners doing the work themselves. No sign-up and no email required. [### Why your Austin HVAC site ranks #4 (and the H1 isn't the fix) Most Austin HVAC sites stuck at #4 in the map pack get diagnosed wrong. It isn't your H1, meta tags, or blog. Here's what actually moves the needle. Read the guide→](/articles/austin-hvac-rank-4-h1-not-the-fix/)4.9191 reviewsWhere this turns into work ## Pages that load before patience runs out Image discipline, restraint with third-party scripts and hosting that answers quickly — fixed at the source rather than patched with a plugin. [See the service→](/services/web-design/)[Ask us about it](/contact/) ![Elvir Sejfulai, Head of Development at Siite](/images/team/panel/elvir-sejfulai.webp) *Our head of development* ## Related entries - [### Quality Score Google Ads' 1-10 diagnostic estimating how relevant your keyword, ad and landing page are to a searcher — better relevance generally means a lower cost per click.](/dictionary/quality-score/) - [### Schema Markup Code added to a page that describes its content in a vocabulary search engines and AI systems read directly — your services, reviews, location, hours and FAQs, stated as data.](/dictionary/schema-markup/) - [### Local Pack The block of three local businesses Google shows above the organic results for searches with local intent, pulled from Google Business Profile data rather than from your website.](/dictionary/local-pack/) [All terms A to Z Browse every term A to Z Open the dictionary→](/dictionary/)