It's probably happened to you. You open a page on your phone, go to tap a button, and right then the content jumps and you end up tapping an ad. Or the page stays blank for several seconds. Those annoyances have a name and a measurement: Core Web Vitals.
They're three metrics Google uses to measure the experience of real people on your site. They're part of the page experience signals Google considers for rankings. They're not the most important factor, since content still rules, but when two pages are similar, experience can tip the scales. Above all, they directly affect whether a visitor stays or leaves.
The three metrics at a glance
| Metric | What it measures | Good | Needs improvement | Poor |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | How long it takes for the main content to appear | Up to 2.5 s | Between 2.5 and 4 s | Over 4 s |
| INP (Interaction to Next Paint) | How quickly the page responds when you tap or click | Up to 200 ms | Between 200 and 500 ms | Over 500 ms |
| CLS (Cumulative Layout Shift) | How much elements move while the page loads | Up to 0.1 | Between 0.1 and 0.25 | Over 0.25 |
These thresholds are the ones Google publishes on web.dev. To pass, at least 75% of visits to a page must fall in the “good” range for each metric.
LCP: the first impression
LCP measures how long it takes for the largest element on the initial screen to appear. It's usually the main photo, a banner, or a large block of text. It's what visitors perceive as “it's loaded.”
What usually hurts LCP
- Heavy or uncompressed hero images.
- Slow hosting that takes a long time to respond.
- Sliders that load several large photos before showing the first one.
- Fonts and styles that block the page from rendering.
The most common fixes are using correctly sized WebP or AVIF images, giving the main image loading priority, enabling caching, and upgrading the server. In many cases, replacing a slider with a single well-chosen image improves both LCP and your message.
INP: how fast it feels
In March 2024, INP replaced the previous metric, FID. It measures the time between an interaction (tapping a button, opening a menu, typing in a form) and the moment the screen shows a response. If you tap “Add to cart” and nothing happens for a second, you have an INP problem.
What usually hurts INP
- Too much JavaScript: chat widgets, tracking pixels, pop-ups, and widgets all running at once.
- Plugins or apps that add code to every page even when it isn't used.
- Heavy, poorly configured page builders.
- Long tasks that block the browser while the person is trying to use the page.
Here, improvement usually comes from removing things. Check which scripts are truly necessary, load the rest only when needed, and organize your tracking tags in Google Tag Manager.
CLS: nothing should jump around
CLS measures visual stability. Every time an element moves without the user asking for it, it adds up. It's the metric behind accidental taps and interrupted reading.
What usually hurts CLS
- Images and videos without a defined width and height.
- Cookie banners or notices that appear at the top and push content down.
- Ads or recommendations inserted after the page loads.
- Web fonts that change the text size once they finish loading.
The fix is to reserve space for each element from the start and display notices in layers that don't push content around. If you use a cookie banner, make sure it doesn't cause layout shifts.
How to measure your Core Web Vitals
There are two types of data, and it's important not to confuse them. Field data comes from real Chrome users and is what Google uses. Lab data is a simulation that's useful for finding the cause of a problem.
- Open Google Search Console and go to the Core Web Vitals report. There you'll see which groups of URLs are doing well and which aren't, on mobile and desktop.
- Run the flagged pages through PageSpeed Insights. Look at the real-user data section first, then the diagnostics.
- Prioritize templates, not individual pages. If the services template fails, every service page fails.
- Apply the fixes, wait a few weeks for the field data to update, and check again.
Key point: If your site gets little traffic, Google may not have enough field data. In that case, use lab data as a guide and focus on a good experience on mid-range phones, which many of your customers use.
Is it worth investing in?
For most businesses, yes, within reason. You don't need a perfect score of 100. You need your important pages in the green and a comfortable experience. A fast, stable site usually means more time spent reading, more messages, and fewer abandoned carts.
If your website is in the red and you don't know where to start, our Core Web Vitals optimization service reviews it template by template. And if you're planning a new site, it's much easier to build it fast from the start; see how we do it in our business website design service. For the full picture of improvements, also check out our guide to website optimization.
Is your site showing red on PageSpeed? We'll help you understand why and fix it with clear priorities.
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