Page speed is how quickly a web page loads, becomes visible, and responds to user input. In SEO the term often also refers to Google’s free testing tool PageSpeed Insights, which measures a URL and suggests improvements. Site speed is the same idea applied to a whole website.
At a glance
- Type
- umbrella term for load time metrics
- Values
- Core Web Vitals LCP, INP, CLS (75th percentile)
- Data sources
- field data (CrUX, 28 days) and lab data (Lighthouse)
- Affects
- user experience; ranking via Core Web Vitals
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How is page speed measured?
No single number captures “load time.” Google measures speed with several metrics. The three Core Web Vitals are Largest Contentful Paint (LCP, when the largest visible element has loaded), Interaction to Next Paint (INP, how quickly the page responds to input), and Cumulative Layout Shift (CLS, how much content moves while loading). Supporting metrics include First Contentful Paint and Time to First Byte.
PageSpeed Insights reports two kinds of data:
- Field data comes from the Chrome User Experience Report (CrUX). It shows how fast the page was for real Chrome users over the previous 28 days.
- Lab data comes from a simulated page load with Lighthouse on a defined device and network. From it, Lighthouse calculates a performance score from 0 to 100.
The two can differ a lot. Field data reflects real devices and connections. Lab data is reproducible and useful for tracing a specific problem.
Does page speed affect rankings?
Google states that Core Web Vitals are used by its ranking systems. According to Google there is no single page experience signal, and relevance comes first. Google Search shows the most relevant content even if its page experience is below average. Where many pages are similarly helpful, good page experience can make a difference.
Example
Google rates each metric at the 75th percentile of page loads:
Assessed at the 75th percentile of page loads, mobile and desktop separately. Sources: web.dev: Largest Contentful Paint (LCP); web.dev: Interaction to Next Paint (INP); web.dev: Cumulative Layout Shift (CLS). Last checked: .
A product page with a field LCP of 3.1 seconds at the 75th percentile needs improvement, even if Lighthouse gives it a lab score of 92.
Common mistakes
- Optimizing only for the Lighthouse score. The score comes from lab data. Google notes that lab data may not capture real-world bottlenecks. Field data shows what real users experience.
- Equating good scores with top rankings. Google says good results in Search Console’s Core Web Vitals report or in third-party tools don’t guarantee top rankings. Relevance comes first.
- Improving a single metric. Google advises site owners not to focus on only one or two aspects of page experience.
- Testing only on desktop. PageSpeed Insights tests mobile and desktop separately, on mobile with a mid-tier phone on a mobile network. The results can differ a lot.
FAQ
What is a good PageSpeed score? In Lighthouse, 90 or higher is good (green), 50 to 89 needs improvement (orange), and below 50 is poor (red). The score is based on lab data.
Why does PageSpeed Insights show no field data for my page? CrUX only includes pages and origins with enough traffic from Chrome users. Without it, PageSpeed Insights shows lab data only.
Is there a free page speed test? Yes. PageSpeed Insights at pagespeed.web.dev is free, and Lighthouse is built into Chrome DevTools.
More on the searchVIU blog
Sources
- About PageSpeed Insights – Google for Developers (last updated 2024-10-21)developers.google.com
- Understanding page experience in Google Search results – Google Search Central (last updated 2026-09-22)developers.google.com
- Web Vitals – web.devweb.dev
- Is PageSpeed Insights reliable? – DebugBear (secondary source)debugbear.com
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