This is one of the most common points of confusion in Core Web Vitals: you run PageSpeed Insights on your page, everything comes up green, and then you open Google Search Console and see that same page listed as "Needs improvement" or "Poor." Which data is correct? The short answer: both are correct, but they measure different things.
The two types of Core Web Vitals data
Lab data
Lab data is synthetic measurement: PageSpeed Insights or Lighthouse simulates a visit to your page under controlled conditions (emulated device, simulated network speed, no cache). It is reproducible, immediate, and useful for technical diagnosis. The problem: it does not reflect the real experience of your actual users.
Field data (CrUX)
Field data comes from the Chrome User Experience Report (CrUX): real measurements from Chrome users who visited your page in the last 28 days. It reflects the actual variety of devices, connections, geographic locations, and user behaviors. This is the data Google uses for ranking.
| Characteristic | Lab Data (PageSpeed/Lighthouse) | Field Data (CrUX/Search Console) |
|---|---|---|
| Source | Controlled simulation | Real Chrome users |
| Time window | Point-in-time measurement | Last 28 days |
| Devices | One emulated device | All devices of your actual users |
| Connection | Fixed simulated network | Real variety of connections |
| Availability | Immediate for any URL | Only if there is sufficient real traffic |
| Used by Google for ranking | ❌ No | ✅ Yes |
| Useful for diagnosis | ✅ Yes | ⚠️ Limited |
Why PageSpeed can show "Good" and Search Console "Poor"
Reason 1: Your users use slower devices than the emulated one
PageSpeed Insights emulates a mid-range device (Moto G Power) with a simulated 4G connection. If a significant portion of your real users use slower devices or slower connections, their real experience will be worse than the simulation. Search Console reflects that real experience.
Reason 2: Field data is the 75th percentile, not the average
Search Console and CrUX report the 75th percentile of each metric — meaning the value that 75% of users experience at that level or better. If only 30% of your users have poor LCP but they are many in absolute terms, the P75 can fall in "Needs improvement" even if the majority of visits are fast.
Reason 3: Recent optimizations have not yet appeared in field data
CrUX aggregates data from the last 28 days. If you made an improvement last week, field data will improve gradually over the next 3 weeks as the 28-day window "forgets" the bad data. PageSpeed, on the other hand, reflects the current state immediately.
Reason 4: URLs grouped in Search Console
Search Console groups similar URLs (for example, all product pages of an ecommerce) and reports the group's status based on a representative URL. If that representative URL has poor CWV, the entire group appears as "Poor" even if most individual URLs are fine.
Why Search Console can show "Good" and PageSpeed "Poor"
This happens less often but is possible. The most common causes: the URL has very little real traffic and CrUX does not have enough data (Search Console does not show the URL or marks it as "good" by default), or the page has very aggressive caching that benefits real users but not the PageSpeed bot, which always loads without cache.
Which data should I prioritize for SEO?
For Google's ranking, field data (Search Console / CrUX) is what matters. If Search Console says "Needs improvement," you have a real SEO problem even if PageSpeed says "Good." Use PageSpeed's lab data to diagnose and find the technical cause, but measure the success of your optimizations in field data.
A page without sufficient field data (low traffic) has no CWV impact on ranking — Google only applies the Page Experience signal when CrUX data is available. This means new or low-traffic pages neither benefit nor are harmed by their CWV scores.
How to use iRankly's Monitor to interpret both types of data
iRankly's Core Web Vitals Monitor uses the PageSpeed Insights API, which shows both field data (CrUX) when available and lab data (Lighthouse). You can see at a glance which of your URLs have discrepancies between both data types and prioritize those with negative field data.
Try the tool for free
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Recommended workflow: (1) Identify pages with poor CWV in Search Console → (2) Analyze those URLs in iRankly's Monitor to see the current state → (3) Use PageSpeed Insights for detailed technical diagnosis → (4) Implement improvements → (5) Verify the impact in field data after 28 days.