Core Web Vitals are a set of metrics defined by Google to measure the quality of a user’s experience while browsing a web page. Officially introduced in 2020, they represent an attempt to go beyond traditional speed indicators based solely on load time, integrating aspects such as responsiveness to input and visual stability of the page. For those working in SEO, these metrics have become a concrete reference because they influence the overall experience of pages and, consequently, can affect ranking in search results.
The metrics that make up Core Web Vitals are three: Largest Contentful Paint (LCP), Interaction to Next Paint (INP) and Cumulative Layout Shift (CLS). Since March 12, 2024, INP has replaced First Input Delay (FID), which is no longer a Core Web Vital. Alongside these are other complementary metrics, such as Time to First Byte and Total Blocking Time, which help diagnose the causes of any problems.
What they measure and why they matter
Core Web Vitals are a subset of Web Vitals metrics, the web performance measurement system proposed by Google. While Web Vitals include numerous indicators, Core Web Vitals focus on three aspects considered fundamental for the user: perceived loading speed (LCP), responsiveness to interactions (INP) and visual stability (CLS). These three dimensions cover the entire page experience, from the arrival of the main content to the use of elements such as buttons and menus.
Core Web Vitals are part of the page experience signals that Google’s ranking systems consider. Google does not declare a precise weight and specifies that relevance and content quality matter more: with equal content, a better experience can help, but a single negative value does not determine a loss of positions.
The three metrics and their thresholds
LCP: when the main content is visible
Largest Contentful Paint, abbreviated LCP, measures the time needed for the largest visible element in the viewport to be rendered. This can be an image, a block of text or a video. A value below 2.5 seconds is considered good, between 2.5 and 4 seconds needs improvement, while over 4 seconds indicates poor performance. To improve LCP, you work on the server, images and resources that block rendering.
INP: responsiveness to all interactions
Interaction to Next Paint, or INP, measures the latency of user interactions (clicks, taps, key presses) throughout the visit and reports the value that represents the slowest interactions. A value of 200 milliseconds or less is considered good, up to 500 milliseconds needs improvement, over 500 milliseconds is poor. It became a Core Web Vital on March 12, 2024, replacing First Input Delay, which only measured the delay of the first interaction. INP depends mainly on the main thread’s workload, which is lightened by reducing unnecessary code and splitting heavy tasks.
CLS: shifts that disturb reading
Cumulative Layout Shift, or CLS, quantifies the unexpected shifting of elements during page load. A score below 0.1 is good, up to 0.25 needs attention, over 0.25 is problematic. Shifts are caused by images without declared dimensions, dynamically inserted ads or fonts that change during rendering. Defining element dimensions and reserving space for dynamic content reduces CLS.
Other useful metrics for diagnosis
In addition to the three main metrics, Google considers some additional metrics useful for diagnosis. Time to First Byte measures the server response time; First Contentful Paint indicates when the first content appears; Total Blocking Time quantifies the time the main thread is busy and not responding to input. These metrics are not part of Core Web Vitals but help identify the causes of a high LCP or INP.
Different tools are used to measure Core Web Vitals. PageSpeed Insights provides both lab and field data, while the Core Web Vitals report in Search Console aggregates real user experiences. Lighthouse, integrated into browsers and developer tools, offers a synthetic assessment under controlled conditions. The web-vitals library allows you to collect metrics directly from users’ browsers.
Metrics compared
| Metric | What it measures | Good value | Poor value |
|---|---|---|---|
| Largest Contentful Paint | Rendering time of the largest visible element | Up to 2.5 seconds | Over 4 seconds |
| Interaction to Next Paint | Latency of interactions during the visit | Up to 200 milliseconds | Over 500 milliseconds |
| Cumulative Layout Shift | Magnitude of unexpected visual shifts | Up to 0.1 | Over 0.25 |
Thresholds apply at the 75th percentile of visits, separately for mobile and desktop. Time to First Byte and Total Blocking Time are not Core Web Vitals: they help understand where a high value comes from.
Where to start to improve performance
Improving Core Web Vitals requires a systematic approach, starting with measurement and continuing with targeted interventions on the identified causes. There is no one-size-fits-all solution: priorities depend on the type of content, the platform used and user behavior. Below are the most common and cross-cutting actions.
- Reduce image weight by using modern formats and adequate compression.
- Always declare image width and height to avoid layout shifts.
- Minimize and defer code not essential for first rendering.
- Use browser caching and a content delivery network.
- Optimize server response time by reducing queries and improving hosting.
- Preload critical resources such as fonts and main images.
- Avoid inserting dynamic content that shifts elements already visible.
- Constantly monitor field data via Search Console and other tools.
Frequently asked questions
Are Core Web Vitals a ranking factor?
They fall within the page experience signals that Google considers, but it does not declare their weight. They matter less than relevance and content quality: they mainly serve to prevent a poor experience from penalizing good content.
Which is the most important of the three metrics?
There is no official hierarchy: Google evaluates all three. LCP is often the most visible because it affects the initial perception of speed.
Do lab data match field data?
Not always. Lab data are collected under controlled conditions, while field data reflect real user experiences, which vary by device, network and geographic location.
How often are the metrics updated?
Google periodically updates metrics and thresholds: on March 12, 2024, INP replaced First Input Delay among Core Web Vitals. The current three are LCP, INP and CLS.
Do Core Web Vitals also apply to mobile sites?
Yes: Search Console and PageSpeed Insights report mobile and desktop data separately, and the thresholds are the same. On mobile, values are often worse due to lower device power and slower networks.
Can a poor score make a page disappear from results?
No, a poor score does not cause a page to be removed from results. It can reduce competitiveness compared to pages with better performance, all other factors being equal.
Do you have this problem?Are your Core Web Vitals scores low and you don’t know where to start optimizing them?Poor scores on LCP, INP and CLS hurt ranking and drive users away. With the Technical SEO Audit we analyze each metric and intervene with targeted solutions.Request the technical audit
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Cls core web vitals Largest Contentful Paint Cumulative Layout Shift Total Blocking Time Lcp google