What Are Core Web Vitals?
Core Web Vitals are three metrics that measure how real users experience a web page: loading, responsiveness and visual stability. They are Largest Contentful Paint (LCP), Interaction to Next Paint (INP) and Cumulative Layout Shift (CLS). A page passes when 75% of visits meet the “good” threshold for all three. Google’s ranking systems use them as part of page experience.
| Metric | Measures | Good | Needs improvement | Poor |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | Loading: when the main content appears | 2.5 s or less | 2.5–4 s | Over 4 s |
| INP (Interaction to Next Paint) | Responsiveness to clicks, taps and key presses | 200 ms or less | 200–500 ms | Over 500 ms |
| CLS (Cumulative Layout Shift) | Visual stability: unexpected movement | 0.1 or less | 0.1–0.25 | Over 0.25 |
The “good” thresholds are from web.dev and Google’s Core Web Vitals documentation. INP replaced an earlier metric, First Input Delay, in March 2024.
What Does Each Metric Measure?
Largest Contentful Paint
LCP marks the moment the largest visible element finishes rendering: usually a hero image, a video poster or a large block of text. It answers “when can I see the main content?”
Interaction to Next Paint
INP measures how long the page takes to respond visually after a user interacts. It considers interactions throughout the visit and reports one of the slowest. It answers “does the page react when I tap?”
Cumulative Layout Shift
CLS adds up unexpected movements of visible content, such as text jumping down when an image or advert loads. It answers “does the page stay still while I read or tap?”
Are Core Web Vitals a Ranking Factor?
Yes, in a limited way. Google says its core ranking systems look to reward content that provides a good page experience, and that Core Web Vitals are used by its ranking systems.
Google also sets clear limits on their importance:
- There is no single page experience signal.
- Good scores do not guarantee top rankings.
- Google always seeks to show the most relevant content, even if page experience is below par.
- Page experience can matter more where many pages offer similar relevance.
- Chasing a perfect score only for SEO may not be the best use of time.
The larger benefit is to users. Faster, steadier pages lose fewer visitors and convert more of them.
Where Do You Find Your Own Data?
Use field data, which comes from real visitors.
| Tool | Data type | Use it for |
|---|---|---|
| Search Console, Core Web Vitals report | Field | Site-wide view; groups of similar URLs; trends |
| PageSpeed Insights | Field and lab | One URL; diagnosis and suggestions |
| Chrome User Experience Report | Field | The public dataset behind the above |
| Browser developer tools | Lab | Debugging on your own machine |
| Real-user monitoring on your site | Field | Detailed, per-page, per-segment data |
Start with the Core Web Vitals report in Search Console. It groups URLs as good, needs improvement or poor, separately for mobile and desktop. Then test a sample URL from each failing group in PageSpeed Insights.
Field data needs enough visits. Low-traffic pages may show no data. In that case, PageSpeed Insights falls back to data for the whole site, or to lab results only.
Why Do Lab and Field Data Differ?
They measure different things.
| Lab data | Field data | |
|---|---|---|
| Source | A simulated test on one device and connection | Real visitors on many devices and networks |
| When | At the moment you run it | Collected over the previous 28 days |
| Interactions | None, or scripted | Real clicks and taps |
| Use | Finding and debugging causes | Judging whether you pass |
| INP | Not measured directly | Measured |
A page can score well in a lab test on a fast connection and fail in the field, because many of your visitors use slower phones. The reverse also happens.
Field data decides whether you pass. Lab data helps you work out why. After a fix, field data takes up to 28 days to reflect it fully.
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See our SEO servicesHow Do You Fix LCP?
Find the LCP element first; PageSpeed Insights names it. Then address the cause.
| Cause | Fix |
|---|---|
| Slow server response | Better hosting, caching, a content delivery network |
| Large hero image | Compress; use modern formats; serve sizes suited to the device |
| LCP image loaded late | Do not lazy-load it; preload it; set high fetch priority |
| Render-blocking CSS and JavaScript | Inline critical CSS; defer non-essential scripts |
| Web fonts delaying text | Use font-display settings; preload key fonts |
| Client-side rendering | Render the main content on the server |
The most common single cause is an oversized image at the top of the page.
How Do You Fix INP?
INP problems come from JavaScript keeping the browser busy.
- Reduce JavaScript. Remove unused libraries and third-party scripts.
- Break up long tasks, so the browser can respond between them.
- Defer non-essential work until after the page is interactive.
- Limit third-party tags: chat widgets, trackers and A/B testing tools are frequent offenders.
- Simplify the page structure. Very large pages take longer to update.
- Give immediate visual feedback on taps, even if the full result takes longer.
INP usually needs a developer. Tag managers make it easy to add scripts and hard to notice their cost; audit them.
How Do You Fix CLS?
CLS comes from elements that arrive without reserved space.
- Set width and height on images and videos.
- Reserve space for adverts, embeds and iframes.
- Do not insert content above existing content, such as banners that push the page down.
- Load fonts carefully, so text does not reflow when the font swaps.
- Use transform animations instead of ones that change layout.
- Check cookie and consent banners; they are a common source.
CLS is often the easiest of the three to fix.
What Should You Fix First?
Prioritise by pages affected and business value.
- Open the Search Console report, and note which groups fail.
- Find the template behind each group. One template fix can repair thousands of URLs.
- Start with templates that drive revenue: product, category and landing pages.
- Within a template, fix the metric rated “poor” before the one that “needs improvement”.
- Test, deploy, and validate the fix in Search Console.
- Wait for field data to update.
Small sites often have one or two templates. Large sites should record results per template.
What Do Core Web Vitals Not Cover?
They are one part of page experience. Google’s self-assessment also asks:
- Are pages served securely, over HTTPS?
- Does content display well on mobile devices?
- Are adverts kept from being excessive or distracting?
- Are intrusive interstitials avoided?
- Can visitors easily tell the main content from everything else?
A page can pass all three metrics and still be unpleasant to use.
Which Mistakes Are Common?
- Optimising for the lab score instead of field data.
- Testing only the home page.
- Testing on a fast desktop when most visitors use phones.
- Lazy-loading the main image.
- Adding a “speed plugin” without measuring what it changed.
- Ignoring third-party scripts because marketing needs them.
- Chasing 100 when the page already passes.
- Expecting a ranking jump from passing.
How Much Effort Is Enough?
Enough to reach “good” for most visitors on your important templates. Beyond that, returns diminish for search, though each further improvement can still help conversion.
If you fail badly on mobile, treat it as a priority. If you pass narrowly, monitor it, and spend the next hour on content. See our guides to page speed and SEO and mobile SEO, and our overview of SEO factors.
Frequently Asked Questions
Are Core Web Vitals a ranking factor?
Google says its ranking systems use Core Web Vitals as part of rewarding good page experience. It also says good scores do not guarantee top rankings and that relevance comes first. Their effect is most likely to show where competing pages are otherwise similar in quality.
What is a good LCP score?
An LCP of 2.5 seconds or less is rated good. Between 2.5 and 4 seconds needs improvement, and over 4 seconds is poor. The target applies at the 75th percentile of page loads, meaning three quarters of real visits should meet it, on both mobile and desktop.
Why do lab and field data differ?
Lab data is one simulated test on a set device and connection. Field data comes from real visitors on many devices and networks over the previous 28 days. Field data decides whether you pass Core Web Vitals. Lab data is for finding the causes of problems.
How long until fixes show in Search Console?
Field data is collected over a rolling 28-day period, so a fix takes up to four weeks to be fully reflected. You can use the “Validate fix” option in the Core Web Vitals report, and check PageSpeed Insights periodically to watch the figures move.
Do I need a perfect PageSpeed score to pass?
No. The PageSpeed performance score is a lab measure and is not the same as passing Core Web Vitals. A page passes when field data for LCP, INP and CLS meets the good thresholds for 75% of visits. Many pages pass with scores well below 100.
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