Lab Data vs Field Data: What “No Data” in PageSpeed Insights Means

Open any PageSpeed Insights report and you’ll see two sections that look like they’re measuring the same thing. Sometimes they agree. Often they don’t. And for many small business sites, the top section just says “No Data”.

Here’s what’s going on, and which numbers deserve your attention.

What is field data?

Field data comes from the Chrome User Experience Report (often called CrUX). Chrome collects anonymous performance data from real users who have opted in to sharing usage statistics. Google aggregates it over a rolling 28-day window.

In PageSpeed Insights, it appears at the top under “Discover what your real users are experiencing”. It shows the Core Web Vitals (LCP, INP and CLS) plus a few supporting metrics, and a simple verdict: the Core Web Vitals assessment passed or failed.

Each metric is reported at the 75th percentile. That means three out of four real visits were at least that good. It’s a deliberately tough standard: your fastest visitors don’t get to hide your slowest ones.

What is lab data?

Lab data comes from Lighthouse, which loads your page once in a controlled environment: an emulated device, a set network speed, a fixed processor speed. It appears in the lower section, “Diagnose performance issues”, with the four familiar scores.

Because it’s a controlled test, it’s repeatable and it comes with diagnostics: a specific list of what’s slowing the page down. That makes it the best tool for fixing things.

Lab data vs field data: the key differences

	Field data	Lab data
Source	Real Chrome users	One simulated visit
Time period	Previous 28 days	Right now
Devices and networks	Whatever your visitors actually use	Fixed, emulated conditions
Includes INP?	Yes	No (uses Total Blocking Time as a stand-in)
Gives fix suggestions?	No	Yes
Used for Google’s Core Web Vitals assessment?	Yes	No

Why does PageSpeed Insights say “No Data”?

Google only shows field data when there are enough real visits from Chrome users who share usage statistics. If a page doesn’t meet that threshold, there’s simply nothing reliable to show.

That’s common for:

• Smaller local businesses
• New websites and new pages
• Individual blog posts and deep service pages
• Sites with mostly desktop or non-Chrome visitors

Sometimes PageSpeed Insights falls back to “origin” data, which is an average across your whole website instead of the specific page. If you see that, remember it’s site-wide, not page-specific.

“No Data” isn’t a penalty and it isn’t a sign something is wrong. Our own homepage showed “No Data” for field data on the day we tested it, alongside perfect 100 lab scores.

Why don’t my lab and field numbers match?

Because they’re measuring different things. A few common reasons for the gap:

Your real visitors have different devices. If most of your customers use older phones on mobile data, field data can be worse than the lab test. If they’re mostly office workers on fast connections, it can be better.

Timing. Field data covers the last 28 days. If you fixed something yesterday, the lab test shows the improvement immediately; field data catches up gradually.

Interactions after loading. Field data includes things that happen while people use the page, like layout shifts when a pop-up appears or slow responses when someone taps a menu. The lab test mostly measures the loading phase.

Caching. Returning visitors often load pages faster thanks to their browser cache. Lab tests simulate a fresh visit.

Which one should you trust?

Both, for different jobs.

Use field data to answer: “How are real customers experiencing my site, and am I passing Google’s Core Web Vitals?”

Use lab data to answer: “What’s slowing this page down, and did my fix work?”

If you have no field data, lab data is your best guide. Aim for good lab scores on mobile and you’ll usually be in good shape when field data does appear.

Where else can you see field data?

Google Search Console has a Core Web Vitals report that groups your pages into good, needs improvement and poor, based on the same real-user data. It’s useful because it shows patterns across many pages at once. We cover it in our Search Console beginner’s guide.

Common mistakes

Panicking about “No Data”. It just means not enough Chrome traffic yet.

Ignoring field data when you have it. If real users are failing Core Web Vitals, that matters more than a good lab score.

Expecting field data to update instantly. Give it a few weeks after a fix.

Only looking at the score. The real value of the lab test is in the diagnostics underneath. Our guide to reading the full report explains how to use them.

Frequently asked questions

What does “No Data” mean in PageSpeed Insights?

Your page doesn’t have enough real visits from Chrome users for Google to report field data. The lab test below still works.

Does Google use lab data or field data for rankings?

Google’s page experience signals use real-user Core Web Vitals, which is field data. Lab data is a diagnostic tool.

How long does field data take to update?

It covers a rolling 28-day period, so improvements show up gradually over several weeks.

Why is my field data worse than my lab data?

Your real visitors may use slower phones or networks than the lab test assumes, or problems may occur after the page loads, such as pop-ups or slow interactions.