Key takeaways
- There are three measures: loading, responsiveness and visual stability.
- They are measured from real visits, so field data matters more than a single test.
- They are one signal among many: a slow page is a poor visit first and a ranking issue second.
Core Web Vitals are three measurements of how a page feels to a real visitor: how quickly the main content appears, how quickly the page responds when you tap or click, and how much the layout jumps while it loads. Search engines use them as one signal among many. Visitors use them to decide whether to stay.
The three measures
| Measure | What it asks | A good result |
|---|---|---|
| Largest Contentful Paint (LCP) | How long until the main content is visible? | 2.5 seconds or less |
| Interaction to Next Paint (INP) | How quickly does the page respond to taps and clicks? | 200 milliseconds or less |
| Cumulative Layout Shift (CLS) | How much does the layout jump around? | 0.1 or less |
The targets are Google's published thresholds, measured at the 75th percentile of real visits, so most of your visitors need to meet them.
Field data and lab data
Field data comes from real visitors and is what search engines use. Lab data comes from a test run on one device and connection, and is useful for finding causes. A page can pass in the lab and fail in the field, particularly on slower phones.
Where the problems usually are
- Slow loading: large uncompressed images, slow servers, and content that waits for scripts before it appears.
- Slow response: heavy scripts that keep the browser busy when the visitor taps.
- Layout jumps: images and embeds without set sizes, late-loading fonts and banners that push content down.
Where to start
- Compress and size images, and load the main one first.
- Give every image and embed a width and height.
- Remove scripts you no longer use, and delay the ones that are not needed at once.
- Serve pages from a fast host or a content network.
- Check the real-user report in Search Console for the page types that fail, and fix the template rather than one page.
A caution
Chasing a perfect score on every page is rarely worth the effort. Fix the templates that carry your traffic, get them into the good range, and move on to work that changes what people find. Page speed is one part of our technical SEO service, and our checklist shows where it sits among the rest.