Core Web Vitals are three Google metrics that describe how fast and stable a page feels to the user: LCP (loading), INP (responsiveness) and CLS (layout stability). The good thresholds are LCP of 2.5 seconds or less, INP of 200 milliseconds or less and CLS of 0.1 or less.

What the three metrics mean

  • LCP (Largest Contentful Paint): how quickly the largest visible element on the page, usually the main image or heading, loads.
  • INP (Interaction to Next Paint): how quickly the page responds when the user presses or taps something.
  • CLS (Cumulative Layout Shift): how much the content jumps about during loading.

Field data tells the truth, a lab test tells the cause

Field data is measured from real visitors. You can see it in the Core Web Vitals report in Search Console and at the top of PageSpeed Insights. This is what Google uses in its assessment.

A lab test such as Lighthouse runs on one device at one moment. It is good for finding a fault but does not tell you what using the website is really like. Do not chase a perfect hundred.

Test the right pages

Do not test only the homepage. Choose one page of each type: the homepage, a service page, an article and the contact page. The same fault repeats on every page that uses the same template.

If LCP is slow

  • The main image is too large or in the wrong format. Use WebP or AVIF at the right size.
  • The main image is lazy-loaded. An image at the top of the view should not be delayed.
  • The server responds slowly. That is a hosting matter.
  • Fonts or styles block the page from rendering.

If INP is slow

The cause is almost always JavaScript. There are too many scripts on the page, and the browser is busy just when the user presses something. Go through the third-party scripts: chats, trackers, embeds. Remove the ones you do not need.

If CLS is high

Something appears late and pushes the content. The usual causes are images without width and height, fonts that load late and a cookie banner that pushes the page down.

Improving speed is part of technical SEO. On WordPress websites the cause is often the theme or the plugins: WordPress SEO. Speed also affects enquiries, which we cover in the conversion tracking guide.

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