Lab data vs field data - what’s the difference?

Lab data and field data are two ways of measuring your site speed, and a speed report usually shows both - they answer different questions, so it helps to know which is which:

• Lab data - a single test run in a controlled environment on a simulated device and connection. Repeatable and great for debugging, but it is one synthetic visit, not your real audience.
• Field data - collected from your actual visitors over the past 28 days on their real devices and networks. This is what Google uses for ranking.
• They can disagree - a fast lab score with poor field data usually means real customers are on slower phones than your test assumed.

Lab data tells you what to fix; field data tells you whether it mattered to real people. When the two disagree, trust the field data - those are your actual customers.