Lab Data vs. Field Data (CrUX)
The difference between a simulated speed test and how your page actually performed for real visitors.
What it means
Lab data comes from a tool like Lighthouse running your page in a controlled, simulated environment — same conditions every time. Field data comes from Chrome's Real User Experience Report (CrUX), which aggregates how the page actually loaded for real visitors on their own devices and connections. The two can disagree, and both are useful for different reasons.
Why it matters
A page can score well in a lab test but perform poorly for real visitors on slow phones or weak connections, or vice versa. Google's ranking systems lean on field data because it reflects genuine user experience, so a good lab score alone doesn't guarantee good field results.
ask datanephew
My Lighthouse score looks fine — why does Search Console flag Core Web Vitals issues?
That's a lab-vs-field mismatch. Ask datanephew to check both — field data from real visitors can surface problems a single lab test on one device doesn't catch.
Which one should I trust more?
Neither alone tells the whole story — ask datanephew to walk through both for a page if the numbers seem to disagree, since each catches something the other misses.