Ever opened a site on your phone, gone to tap a button and watched the page jump at the last second? Or waited for the main image and gave up first? That is exactly what Core Web Vitals measure. They are three numbers Google uses to judge whether a page feels good, and they track closely with how many people stay and buy.
The three metrics
Google sets the targets like this on web.dev:
| Metric | What it measures | “Good” target |
|---|---|---|
| LCP (Largest Contentful Paint) | How long the biggest visible element (headline, hero image) takes to show up | 2.5 seconds or less |
| INP (Interaction to Next Paint) | How long the page takes to react when someone taps or clicks | 200 milliseconds or less |
| CLS (Cumulative Layout Shift) | How much the layout jumps unexpectedly while the page is in use | 0.1 or less |
A page only passes if it hits all three at the 75th percentile of visits, with mobile and desktop counted separately. Your site being fast on your own laptop is not enough. Three out of four real visitors need that experience.
INP is the newest. It replaced the old FID and became a stable metric in 2024, because it measures the response to every interaction, not just the first one.
Does it affect Google rankings?
Yes, though not the way it is often sold. Google Search Central “highly recommends” good Core Web Vitals and says they align with what its ranking systems aim to reward. Relevant content still comes first. A fast, empty site will not outrank a slower one that answers the question better.
My practical take: speed will not rescue weak content, but it can break a tie. And in SEO, tie-breakers are worth money.
Where the money shows up
The strongest argument is your customers, not Google. Rakuten 24, the Rakuten group’s online store in Japan, ran a one-month A/B test: half the visitors got a page optimized for Core Web Vitals and half got the original. Performance was the only difference. The results, from the web.dev case study:
- +33.13% conversion rate
- +53.37% revenue per visitor
- +15.20% average order value
- −35.12% exit rate
Other cases Google collected point the same way. Vodafone Italy improved LCP by 31% and sold 8% more. Tokopedia improved LCP by 55% and saw 23% longer sessions.
A caveat: these numbers were published by the companies themselves, and your result depends on your audience. The direction is consistent, though.
Measuring without fooling yourself
Core Web Vitals are field metrics first, collected from real visits. Lab tools like Lighthouse help you find problems but do not replace real data. web.dev points out that Lighthouse cannot even measure INP, since nobody is clicking during the test.
A simple routine:
- Run PageSpeed Insights on your URL. If it shows real-user data (“Discover what your real users are experiencing”), read that part first.
- Open the Core Web Vitals report in Google Search Console to see which pages fail at scale.
- Only then use Lighthouse to dig into the cause of each issue.
The usual suspects
- Slow LCP: a heavy hero image in an old format, with no set size or loaded late. A web font that blocks rendering.
- Slow INP: too much JavaScript running at once, usually from plugins, third-party chat widgets and ad scripts.
- High CLS: images and banners with no reserved space, a font that changes size when it loads, a cookie notice that pushes content down.
On this site, for example, I measured in a local test an LCP of about one second and zero CLS on a simulated phone with a 4G connection and a CPU four times slower. No magic involved: modern image formats, little JavaScript and reserved space for everything that loads later.
If your site is in the red, the hero image and third-party scripts are a good place to start.
Sources
- Web Vitals. web.dev (Google). accessed October 2026.
- Understanding Core Web Vitals and Google search results. Google Search Central. accessed October 2026.
- How Rakuten 24's investment in Core Web Vitals increased revenue per visitor by 53.37% and conversion rate by 33.13%. web.dev (Google), updated 2022-08-24. accessed October 2026.
- The business impact of Core Web Vitals. web.dev (Google), updated 2021-09-01. accessed October 2026.