Measuring Speed: Lab vs Field Data
There are two ways to measure how fast a site is, and they answer different questions. Lab data comes from a controlled test; field data comes from your real visitors. You need both to get the full picture.
Confusing the two is a common source of misunderstanding when reading performance reports.
Why the Two Can Disagree
It is common for a lab score to look better than the real-world one, and understanding why prevents false confidence. Real visitors use a huge range of devices and connections that a single test cannot capture.
- Lab tests often run on fast hardware and networks.
- Field data includes older phones and weak signals.
- A page can pass in the lab yet struggle in the field.
- Google ranks on the real-visitor figures.
How We Use Both Together
Lab and field data are most powerful in combination. Field data tells us where real visitors are struggling, and lab tools let us reproduce and fix the problem in a controlled way before confirming the result back in the field.
- Watch field data to spot which pages and metrics need attention.
- Use lab tests to diagnose the underlying cause.
- Make and verify the fix in the lab first.
- Confirm the improvement reaches real visitors over time.
The Difference
Lab tests are repeatable and great for diagnosing problems. Field data reflects the messy reality of different devices, locations and connection speeds.
| Lab data | Field data | |
|---|---|---|
| Source | Controlled test | Real visitors |
| Good for | Debugging changes | True experience |
| Example tool | Lighthouse | Search Console / CrUX |
Frequently Asked Questions
Why does my lab score look better than my real one?
Lab tests often run on a fast machine and connection. Your field data includes older phones and slower networks, which is what most visitors actually use.
Which should I trust for ranking?
Google uses field data from real Chrome users for the page experience signal, so that is the score that affects rankings.
If you need a hand with any of this, your Progressive Robot delivery team is ready to help. Raise a ticket from the Support area of your client portal or speak to your account manager and we will guide you through the next steps.