What do the three measurements mean?
Each one answers a question a visitor would ask.
- Largest Contentful Paint: when can I see the main thing? Good is under 2.5 seconds.
- Cumulative Layout Shift: does the page jump as it loads? Good is under 0.1.
- Interaction to Next Paint: does it respond when I tap? Good is under 200 milliseconds. Lab tests use Total Blocking Time as a stand-in.
What usually makes a page slow?
Large images are the most common cause, followed by scripts that must download and run before anything is shown, and slow hosting that takes a second or more just to answer.
Which fixes make the biggest difference?
Start with the ones that cost least.
- Resize and compress images, and use a modern format such as WebP or AVIF.
- Give every image a width and height, so the page does not shift as images arrive.
- Add defer or async to scripts so they do not hold up the page.
- Turn on compression (gzip or Brotli) and caching on the server.
- Remove scripts and plugins you no longer use.
Why do results differ between tests?
A lab test loads the page once on one machine, so results vary from run to run and between tools. Google's own ranking data comes from real visitors over 28 days. Use lab tests to find problems and to check a fix, not as an exact score.