Core Web Vitals Explained: The Metrics Google Uses to Rank Your Site

What Are Core Web Vitals and Why Should You Care

Google does not rank websites based on gut feeling. It measures real-world user experience through a set of three specific metrics called Core Web Vitals. These numbers reflect how fast your page loads, how quickly it responds to interaction, and how visually stable the content remains while rendering.

If you run a business in the Valley and depend on search traffic to bring customers through the door, these metrics directly affect your bottom line. Google uses Core Web Vitals as a confirmed ranking signal. Two sites with comparable content and authority will see the faster, more stable site rank higher. That is not speculation. Google published the page experience update in 2021 and has refined the measurement criteria since then.

The good news is that Core Web Vitals are not abstract. They are measurable, improvable, and concrete. You do not need to be an engineer to understand what they mean. You do need to understand them if you want your website to compete in organic search.

LCP: Largest Contentful Paint

Largest Contentful Paint measures how long it takes for the main visible content on your page to finish loading. This is typically the hero image, a large heading, or a featured video thumbnail. It answers a simple question: when does the visitor actually see something useful?

Google defines three thresholds for LCP:

Good: Under 2.5 seconds
Needs improvement: Between 2.5 and 4 seconds
Poor: Over 4 seconds

A slow LCP usually stems from a handful of common problems. Oversized images are the most frequent culprit, especially on small business sites where someone uploaded a 4MB photo straight from their phone. Slow server response times also contribute, particularly if your hosting plan is underpowered for your traffic. Render-blocking CSS and JavaScript files can delay the browser from painting anything on screen until those resources finish downloading.

In practice, fixing LCP often comes down to three actions: compress and properly size your images, use a content delivery network to serve assets from a location close to your visitors, and eliminate or defer render-blocking resources. For an Arizona business serving a local audience, a CDN with edge nodes in Phoenix makes a measurable difference compared to hosting everything on a single server in Virginia.

INP: Interaction to Next Paint

Interaction to Next Paint replaced First Input Delay (FID) as a Core Web Vital in March 2024. While FID only measured the delay of your first click or tap, INP tracks responsiveness across every interaction during the entire page visit. It captures the worst-case latency between a user action and the visual update that follows.

The thresholds for INP are:

Good: Under 200 milliseconds
Needs improvement: Between 200 and 500 milliseconds
Poor: Over 500 milliseconds

Think about what happens when a customer taps your navigation menu on their phone and nothing appears for half a second. Or they click “Add to Cart” and the button sits there frozen. That delay erodes trust. Users interpret sluggish responses as a sign that something is broken, and they leave.

INP problems typically trace back to heavy JavaScript execution on the main thread. Third-party scripts are a common source: analytics trackers, chat widgets, ad scripts, and social media embeds all compete for the same processing time that your page needs to respond to user input. Every script you add to your site is a potential drag on interactivity. For instance, a restaurant site in Tempe running four third-party widgets may score well on loading speed but fail INP because those scripts block the browser from processing tap events in time.

The fix usually involves auditing your third-party scripts, lazy-loading anything that is not immediately essential, and breaking up long-running JavaScript tasks so the browser can respond to user input between chunks of work.

CLS: Cumulative Layout Shift

Cumulative Layout Shift measures visual stability. It quantifies how much the visible content moves around while the page is loading. If you have ever tried to tap a link on your phone only to have the page jump and send you somewhere else, you have experienced a layout shift.

Google’s thresholds for CLS are:

Good: Under 0.1
Needs improvement: Between 0.1 and 0.25
Poor: Over 0.25

The score is unitless. It is calculated by multiplying the fraction of the viewport that shifted by the distance the content moved. A score of zero means nothing shifted at all. Anything above 0.25 means visitors are dealing with a visually unstable experience.

Common causes of layout shift include images and videos without explicit width and height dimensions, ads or embeds that inject themselves into the page after initial render, and web fonts that swap in with different sizing than the fallback font. On many small business sites, the biggest offender is a banner image at the top of the page that loads without reserved space. The text below it renders first, then the image arrives and pushes everything down. That single shift can blow your CLS score.

Preventing CLS requires setting explicit dimensions on all media elements, reserving space for ad slots and dynamic content before they load, and using the font-display: swap property carefully with size-adjusted fallback fonts. These are straightforward changes that produce immediate results.

What “Good” Scores Look Like

Google evaluates your Core Web Vitals at the 75th percentile of page loads. That means 75% of your visitors need to have a good experience for your site to pass. It is not enough for the page to load fast on your MacBook Pro connected to fiber. The metric reflects how real users on real devices experience your site, including the customer browsing on a three-year-old Android phone over a cellular connection in Gilbert.

Here is a summary of the thresholds:

LCP: Good under 2.5s, needs improvement 2.5-4s, poor over 4s
INP: Good under 200ms, needs improvement 200-500ms, poor over 500ms
CLS: Good under 0.1, needs improvement 0.1-0.25, poor over 0.25

Passing all three at the 75th percentile earns your page the “good” designation in Google Search Console. Pages that fail one or more metrics receive “needs improvement” or “poor” labels. Google groups these assessments by URL pattern, so a slow blog template can drag down every post on your site.

How to Check Your Scores

You do not need to hire a developer to see where your site stands. Google provides several free tools that report Core Web Vitals data.

PageSpeed Insights

Visit pagespeed.web.dev and enter your URL. The tool runs a Lighthouse audit and, when available, shows field data from the Chrome User Experience Report. Field data reflects actual visitor experiences. Lab data simulates a controlled test. Both are useful, but field data is what Google uses for ranking decisions.

Google Search Console

If you have Search Console connected to your site, the Core Web Vitals report groups your URLs by status. It tells you exactly which pages pass and which ones need work, along with the specific metric that is failing. This is the most actionable view because it ties directly to how Google perceives your pages.

Chrome DevTools

Open Chrome, press F12, and navigate to the Performance tab. You can record a page load and inspect LCP, CLS, and INP in real time. The Lighthouse tab in DevTools also runs a full audit. However, keep in mind that DevTools results are lab measurements from your own machine, not field data from real users. They are helpful for debugging but should not be treated as your final score.

Common Problems and Quick Fixes

Most Core Web Vitals failures trace back to a short list of recurring issues. Here are the problems we see most often when auditing sites for Arizona businesses, along with the fixes that produce the fastest improvement.

Slow LCP

Unoptimized images: Convert to WebP or AVIF format, set explicit width and height attributes, and use responsive srcset so mobile devices receive smaller files.
No CDN: Serve static assets through a content delivery network. A CDN caches your files on servers geographically close to your visitors, cutting round-trip time significantly.
Render-blocking resources: Defer non-critical CSS and JavaScript. Inline the critical CSS needed for above-the-fold content so the browser can paint immediately.

Poor INP

Too many third-party scripts: Audit every external script on your page. Remove anything you are not actively using. Defer or lazy-load the rest.
Long JavaScript tasks: Break heavy processing into smaller chunks using requestIdleCallback or setTimeout so the browser stays responsive between operations.
Unoptimized event handlers: Debounce scroll and resize listeners. Avoid running expensive DOM queries on every keystroke in search inputs.

High CLS

Images without dimensions: Always include width and height on <img> tags. Modern frameworks like Next.js handle this automatically when you use their image components.
Late-loading ads and embeds: Reserve fixed space in your layout for dynamic content so it does not push other elements around when it appears.
Font swap shifts: Use font-display: optional or configure size-adjusted fallback fonts to minimize the visual jump when custom fonts load.

How This Affects Your Google Rankings

Google introduced Core Web Vitals as a ranking signal in June 2021 as part of the page experience update. The signal applies to all search results and is evaluated on a per-page basis using field data from real Chrome users.

It is worth noting that Core Web Vitals are one factor among many. Relevant, high-quality content still matters more than raw speed. However, when two pages compete for the same search query with similar content quality and backlink profiles, the page with better vitals will rank higher. For competitive local keywords in the Phoenix metro area, that edge can mean the difference between appearing on page one and being buried on page two.

Google also uses mobile-first indexing, meaning it evaluates the mobile version of your site for ranking purposes. If your desktop site scores well but the mobile experience is slow or unstable, your rankings reflect the mobile performance. Given that most local searches happen on phones, this is especially relevant for brick-and-mortar businesses in Arizona that depend on nearby customers finding them through search.

Beyond rankings, Core Web Vitals correlate with user behavior that search engines care about. Faster, more stable pages see lower bounce rates, longer session durations, and higher conversion rates. These engagement signals reinforce your search position over time. A site that loads quickly and responds to taps without delay keeps visitors engaged, and engaged visitors send positive behavioral signals back to Google.

Want to know where your site stands? Schedule a conversation and we will walk through your Core Web Vitals scores together.