Core Web Vitals
Core Web Vitals are three measurements Google defines for how a page feels to a visitor: how soon the main content appears, how fast the page reacts, and whether the layout stays still. They are taken from real visits in Chrome, not from a test.
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In short
- The three are LCP, INP and CLS. Good is 2.5 seconds or less, 200 milliseconds or less, and 0.1 or less.
- A page passes when all three are good for three visits in four, counted over the previous 28 days, on phones and on desktops separately.
- The score out of 100 is a lab figure and is not one of them. When the score and the assessment disagree, the assessment is the one based on real visitors.
Core Web Vitals are three measurements Google defines for how a page feels to the person using it.
| Metric | What it measures | Good | Poor |
|---|---|---|---|
| Largest Contentful Paint (LCP) | Loading: how long until the largest image, video or block of text in view is drawn | 2.5 seconds or less | Over 4 seconds |
| Interaction to Next Paint (INP) | Responsiveness: how long the page takes to respond to a click, a tap or a key press | 200 milliseconds or less | Over 500 milliseconds |
| Cumulative Layout Shift (CLS) | Visual stability: how much the content moves when the visitor did not cause it | 0.1 or less | Over 0.25 |
Anything in between needs improvement. Each figure is judged at the 75th percentile: three visits in four must be at or under the good threshold. Phones and desktops are judged separately. A page passes when all three are good.
The figures are field data. Chrome collects them from real visits, and Google publishes them for pages and sites with enough visits, covering the previous 28 days. A lab test is something else: one load of the page on one simulated device, used to find causes. It cannot measure INP, because nobody clicks anything during it.
Where you meet it
- PageSpeed Insights, at pagespeed.web.dev, shows the field data for one page and says whether it passes the Core Web Vitals assessment. A page with too few visits is given the figures for the whole site. A site with too few gets no field data at all. Below that is the lab test, with its score out of 100.
- Search Console has a report named "Core Web Vitals", for mobile and desktop. It puts similar pages into groups and labels each group "Poor", "Need improvement" or "Good", by its worst metric.
- WordPress has no screen for them. Site Health checks the server's response time and whether there is a page cache. It measures none of the three figures.
What goes wrong
- LCP fails. The server answered late, or the main image started late or arrived slowly. See how to fix Largest Contentful Paint. The terms to know are TTFB, lazy loading and render-blocking resources.
- INP fails. Long tasks keep the browser busy when the visitor taps or clicks. See how to fix Interaction to Next Paint.
- CLS fails. An image, a video, an ad or a font arrives and takes up space that was not reserved for it. See how to fix Cumulative Layout Shift.
- The score is high and the assessment fails. The score comes from one lab load. The assessment comes from real visitors, on their own phones and connections.
- A fix shows no change. The field figures cover 28 days, so they move slowly. Check the change in the lab test, then read the field data again some weeks later.
How to improve WordPress Core Web Vitals covers all three in order. If you are pricing the work, what WordPress speed optimization costs sets out what the job should include.
Common questions
Do Core Web Vitals affect Google rankings?
Google's Search documentation advises site owners to get good Core Web Vitals, both to do well in Search and for their visitors' sake. It describes them, together with the rest of page experience, as in line with what its core ranking systems reward. That page puts no figure on the effect.
Is the PageSpeed score one of the Core Web Vitals?
No. The score out of 100 is worked out from a single lab load of the page. The Core Web Vitals are three field figures from real visits.
What happened to First Input Delay?
Interaction to Next Paint replaced First Input Delay (FID) as a Core Web Vital on March 12, 2024. Advice written about FID is out of date.