SEO

Speed test (website)

Q: What is the difference between a speed test and Core Web Vitals?

A speed test is a single test run that measures, among other things, the Core Web Vitals values. The Core Web Vitals are the three specific metrics (LCP, CLS, INP) that Google uses as a ranking signal. Alongside the Core Web Vitals, a speed test also covers SEO, Accessibility and Best Practices scores plus diagnostic audits.

Q: Is lab data enough for SEO?

No. For ranking, Google uses only field data from the Chrome User Experience Report (CrUX), measured at the 75th percentile over 28 days of real users. Lab data from a speed test is a diagnostic tool for identifying improvements — an improvement only affects rankings once it is reflected in the field data.

Q: How often should I run a speed test?

With every major code or asset change — a new hero image, a new JavaScript library, a theme update. Plus monthly as a routine check. Tools such as Rankmio keep the history over time and raise an alert when a score drops significantly.

Also known as: Page speed test, Website speed test, PageSpeed test, Performance test

A speed test for a web page measures how quickly the browser can load, render and make a page usable. In an SEO context, ”speed test” usually refers to a run against the Google PageSpeed Insights API or the underlying Lighthouse — both return four scores (Performance, SEO, Accessibility, Best Practices) on a scale from 0 to 100, plus the three Core Web Vitals LCP, CLS and INP/TBT. Since 2021 these values have fed into Google rankings as a page experience signal.

What a speed test typically measures

Performance score (0–100) — aggregated from render times, interactivity and layout stability.
LCP (Largest Contentful Paint) — when does the largest visible element appear? The ”good” threshold is < 2.5 s.
CLS (Cumulative Layout Shift) — how much does the layout jump around while loading? ”Good” threshold: < 0.1.
INP / TBT (Interaction to Next Paint / Total Blocking Time) — how does the page respond to input? INP has been the official metric since March 2024.
FCP (First Contentful Paint) — when does the first visible element appear?
SEO, Accessibility and Best Practices scores — Lighthouse heuristics covering meta tags, schema markup, alt attributes and security headers.

Lab data versus field data

A speed test delivers lab data: a single test run in a controlled environment, reproducible but not representative. Field data comes from the Chrome User Experience Report (CrUX) and contains real user values over 28 days. Only the field data at the 75th percentile counts for Google rankings — the lab values from a speed test are a diagnostic tool, not a ranking signal.

Speed test tools in 2026

Google PageSpeed Insights — the official tool, showing lab and field data in a single view.
Lighthouse — built into Chrome DevTools, using the same method as PageSpeed Insights, lab data only.
WebPageTest — more granular, with a waterfall chart, several locations and optional real devices.
Rankmio free speed test tool (/seo-tools/speedtest) — lab score via the PageSpeed Insights API, mobile and desktop in one run.
Rankmio Site Audit — embeds PageSpeed data in a complete on-page/GEO assessment and keeps the history over time.

Example from practice

Example: A shop runs with a mobile performance score of 48 (lab) and an LCP of 4.1 s. The hero image is 2.3 MB in size and is not preloaded. After compression to WebP (180 KB), fetchpriority="high" and a preload hint, LCP falls to 1.9 s and the lab score rises to 84. In the CrUX field data the values improve measurably after 4 weeks — the LCP 75th percentile moves from ”needs improvement” to ”good”. Ranking effect after 8 weeks: three top 10 keywords each improve by one position.

Frequently asked questions

What is the difference between a speed test and Core Web Vitals?

A speed test is a single test run that measures, among other things, the Core Web Vitals values. The Core Web Vitals are the three specific metrics (LCP, CLS, INP) that Google uses as a ranking signal. Alongside the Core Web Vitals, a speed test also covers SEO, Accessibility and Best Practices scores plus diagnostic audits.

Is lab data enough for SEO?

No. For ranking, Google uses only field data from the Chrome User Experience Report (CrUX), measured at the 75th percentile over 28 days of real users. Lab data from a speed test is a diagnostic tool for identifying improvements — an improvement only affects rankings once it is reflected in the field data.

How often should I run a speed test?

With every major code or asset change — a new hero image, a new JavaScript library, a theme update. Plus monthly as a routine check. Tools such as Rankmio keep the history over time and raise an alert when a score drops significantly.

Used in Rankmio for

Free speed test with Google PageSpeed Insights

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Last updated: 2026-06-30 · Browse all glossary entries