How Core Web Vitals & Lighthouse scores affect SEO Rankings - Vercel

Understanding Core Web Vitals and Their Impact on Google Ranking

Core Web Vitals influence how your application's pages rank on Google. Here, we'll dive into what they are, how they’re measured, and how your users and search ranking are impacted by them.

Malte Ubl is the CTO of Vercel and former Director of Google Search responsible for shipping the “Page Experience” ranking rollout—which heavily utilizes Core Web Vitals. That said, everything written here is publicly documented and linked where appropriate.

How Google Ranks Based on Page Speed

Your site’s ranking in Google Search is impacted by Google’s page experience ranking system, which evaluates the performance of your site based on Google’s Core Web Vitals metrics.

Google collects Core Web Vitals by observing how real users interact with your website and reporting that back to its servers. This type of data is called field data because it gets collected from real users browsing your site. This is different from lab data, which is the result of tests run in a "lab setting" to determine how well your site performs. Google’s Lighthouse is an example of a lab test.

The most important takeaway is:

“Google only considers the Core Web Vitals field data when ranking your site. Google does not consider your Lighthouse score in any way for search ranking.”

Contextualizing Search Ranking Factors

Page experience is a ranking factor in Google Search that utilizes Core Web Vitals to determine how your website performs relative to other sites. Page experience is one of many ranking factors in Google Search, which all get aggregated together to determine your site's ranking on a search result page.

Relevancy to the query and quality of the content are substantially more important factors than page experience. However, when you and your competitors have very similar relevancy, page experience may decide who comes out on top.

Core Web Vitals are unique in that they can be improved through your own work and Google is transparent about how well you’re doing. Their optimization involves less guesswork than improving relevancy and is easier to measure than content quality.

Improving Core Web Vitals directly impacts user experience, which drives conversion.

How to See Your Application’s Core Web Vitals

The authoritative data source for how well your entire app performs for page experience rankings is Google Search Console.

The Core Web Vitals page of Google Search Console.

You can also access per-page data through Google’s PageSpeed Insights, which is grouped into two main sections: Core Web Vitals and Lighthouse.

Field Data: Core Web Vitals

Google collects global field data of the 75th percentile of actual users who have accessed your application in the past 28 days from Chrome browser (desktop and Android mobile devices). The three main metrics are Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS). Note that as of March 12, 2024, INP has replaced First Input Delay (FID).

These three Core Web Vitals are the only data Google uses to affect the rank of your app based on its web performance.

The mobile Core Web Vitals for google.com.

Users Included in Core Web Vitals Field Data

The Chrome User Experience Report (CrUX) is the official dataset of Google’s Core Web Vitals program. To be included, pages must be:

Users must also enable usage statistic reporting and use Chrome on either desktop or Android.

Does It Matter Where My Users Are Coming From?

Yes, it does matter where your users are coming from as field data reflects your real users. However, internet connectivity and device performance have been improving worldwide.

Caveat: 28-Day Sliding Window

Google collects Core Web Vitals data on a 28-day sliding window, meaning it can take time to evaluate the impact of changes.

Lab Data: Lighthouse

In the second section of PageSpeed Insights, Google simulates the performance of your application using Lighthouse, which offers suggestions for improvement but does not affect your search ranking.

The mobile Lighthouse scores for google.com.

Interpreting Your Lighthouse Scores

Lighthouse provides useful information that can help you identify performance-related issues, accessibility errors, best practices, and technical SEO advice.

A Quicker Way to Iterate on Core Web Vitals: Vercel Speed Insights

Vercel created Speed Insights to provide real-time data on your Core Web Vitals, allowing prompt responses to performance issues.

A snapshot of the Speed Insights tab from the project view.

Further Reading: Optimizing Core Web Vitals

Explore our deep dive into optimizing Core Web Vitals, along with Google’s technical guides on Largest Contentful Paint (LCP), Cumulative Layout Shift (CLS), and Interaction to Next Paint (INP).

Takeaways