What are Core Web Vitals?
They're three measures Google uses to judge page experience: loading, responsiveness and visual stability. Each one has a "good" mark set by Google, and a page passes when real visits meet all three.
They come up in almost every website audit, usually as a wall of red and amber. The idea behind them is simple: does the page show up quickly, does it respond when you use it, and does it stay still while you read it.
What do LCP, INP and CLS mean?
Here's each one, with Google's own pass marks.
- Largest Contentful Paint (LCP) measures how long the largest image or block of text in view takes to appear. Good is 2.5 seconds or less. Over 4 seconds is poor.
- Interaction to Next Paint (INP) measures how long the page takes to respond visibly after someone taps, clicks or types, across the whole visit. Good is 200 milliseconds or less. Over 500 milliseconds is poor.
- Cumulative Layout Shift (CLS) measures how much content moves unexpectedly while the page loads. Good is 0.1 or less. Over 0.25 is poor.
What happened to First Input Delay?
INP replaced First Input Delay (FID) as a Core Web Vital in March 2024. FID only measured the first interaction. INP looks at responsiveness across the whole visit, so it's a stricter test. Older reports and articles may still mention FID.
How does Google measure Core Web Vitals?
With real visits, not a lab test. Google uses data from Chrome users and looks at the 75th percentile, separately for mobile and desktop. In plain terms, a page passes only if at least three quarters of visits have a good experience.
That's why a site that feels fast on office broadband can still fail on a customer's phone. PageSpeed Insights shows both kinds of data: field data from real visits at the top, where Google has enough, and a lab score out of 100 below it. The field data is what Google uses. Search Console's Core Web Vitals report groups your pages by whether they pass.
How much do Core Web Vitals matter for rankings?
Less than some audits suggest, and more than none. Google says its ranking systems use them, but also that it will still show the most relevant page even if its page experience isn't great.
So a fast page with a thin answer won't beat a slower page that answers the question well. The stronger reason to fix them is commercial: a page that's slow to show anything, or jumps as someone goes to tap "Buy", loses customers whatever its ranking.
How do you improve Core Web Vitals?
Work in this order. The early steps usually make the biggest difference for the least effort.
- Open Search Console's Core Web Vitals report and note which groups of pages fail, on mobile first.
- Test one page from each failing group in PageSpeed Insights and note which measure fails.
- For LCP, fix the main image: resize it to the size it's shown at, compress it, use a modern format and don't lazy-load it.
- Still slow? Check the server response. Slow hosting holds up everything else.
- For INP, list every third-party script, from chat widgets to old tracking tags, and remove what you don't use.
- For CLS, reserve space for images, embeds, adverts and banners so nothing pushes the content down when it arrives.
- Make the changes, then use Search Console to start validation and check the field data over the following weeks.
Should you chase a perfect score?
No. Get the field measures into the good range and move on. Pushing a lab score from good to perfect rarely changes anything a customer would notice.
Speed does slip over time, though. New plugins, big images and campaign tags creep in. Check the Search Console report every month, and build speed into the brief for any redesign.