What are the Core Web Vitals thresholds in one place?

LCP good at 2.5 seconds or under; CLS good at 0.1 or under; INP good at 200 milliseconds or under. Beyond each is needs-improvement, then poor.

Do Core Web Vitals affect Google ranking?

Yes, they're part of Google's page-experience signals — but they're one factor among many. Great performance won't outrank genuinely better content, and it won't save a page that's blocked or thin. Treat CWV as table stakes, not a silver bullet.

Why did INP replace First Input Delay?

INP looks at the responsiveness of all interactions across the whole visit, not just the first one, so it's a more complete picture of how the page feels to use. It became the standard responsiveness Vital in 2024.

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Core Web Vitals in plain English

Core Web Vitals are three metrics for loading, visual stability, and responsiveness — LCP, CLS, and INP. Here's what each means and the exact thresholds Sight grades against.

Updated 2026-07-19

Core Web Vitals are three metrics Google uses to measure the real-world experience of loading a web page: how fast the main content appears, how much the layout jumps around while it loads, and how quickly the page responds when you interact with it. They're named LCP, CLS, and INP. Together they're a proxy for "does this page feel fast and stable to a human," and they're a ranking signal — so they matter for SEO as well as for the people actually using your site.

Sight measures all three per page and grades each against Google's published good and needs-improvement boundaries. Here's what they mean and where the lines are.

What is Largest Contentful Paint (LCP)?

LCP measures loading: the time from when navigation starts to when the largest visible element in the viewport — usually your hero image, a headline, or a big block of text — has rendered. It answers "how long until the page looks basically ready?"

Sight's LCP check grades 2.5 seconds or under as good, up to 4 seconds as needs-improvement, and slower than that as poor. The usual culprits behind a slow LCP are an unoptimized hero image, render-blocking CSS or JavaScript, and slow server response. The fixes are correspondingly concrete: compress and preload the hero image, cut render-blocking resources, and put a CDN in front of your assets.

What is Cumulative Layout Shift (CLS)?

CLS measures visual stability: how much the page's content unexpectedly moves around as it loads. You've felt bad CLS when you go to tap a button and an image finishes loading above it, shoving everything down so you tap the wrong thing. It's scored as a unitless number, not a time.

Sight's CLS check grades 0.1 or under as good and up to 0.25 as needs-improvement. The classic cause is elements that load without reserved space — images and embeds with no declared width and height, or content injected above existing content. Reserve space explicitly (set width and height on images, size your ad and embed slots) and avoid pushing content down after the page has started rendering.

What is Interaction to Next Paint (INP)?

INP measures responsiveness: when a user interacts — a tap, a click, a keypress — how long until the page visibly responds. High INP is the "I clicked and nothing happened" feeling, usually caused by heavy JavaScript blocking the main thread. Sight's INP check grades 200 milliseconds or under as good and up to 500 milliseconds as needs-improvement. The fixes: break up long JavaScript tasks, defer non-critical scripts, and keep event handlers light.

One honest caveat on INP: it reflects real user interactions, so it's a field-data metric. When Sight has real-world (field) data available for your site it uses that; otherwise INP may not be measurable in a lab pass, and the check reports accordingly rather than guessing.

How does Sight measure these?

Sight measures Core Web Vitals two ways, preferring real over synthetic. When a PageSpeed Insights data source is available, it uses that — which includes real-world field measurements from actual visitors. When it isn't, Sight falls back to a lab measurement: it loads the page in a real headless browser and records the metrics directly. Either way you get the same three numbers graded against the same thresholds, so the report reads consistently. Because performance is measured per page, a fast home page won't hide a slow product page — each URL is graded on its own.

What are the Core Web Vitals thresholds in one place?: LCP good at 2.5 seconds or under; CLS good at 0.1 or under; INP good at 200 milliseconds or under. Beyond each is needs-improvement, then poor.
Do Core Web Vitals affect Google ranking?: Yes, they're part of Google's page-experience signals — but they're one factor among many. Great performance won't outrank genuinely better content, and it won't save a page that's blocked or thin. Treat CWV as table stakes, not a silver bullet.
Why did INP replace First Input Delay?: INP looks at the responsiveness of all interactions across the whole visit, not just the first one, so it's a more complete picture of how the page feels to use. It became the standard responsiveness Vital in 2024.

The takeaway

Three numbers: LCP under 2.5s, CLS under 0.1, INP under 200ms. They map to loading, stability, and responsiveness — the three things that make a page feel good or bad to a real person. Fix the worst one first, measure again, and remember that performance is a supporting act: it earns you the click; your content has to keep it. For how to sequence performance work against everything else, see prioritizing SEO fixes.

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