Core Web Vitals are three metrics — Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness) and Cumulative Layout Shift (visual stability) — that Google uses to measure real-world page experience and factor into rankings.
Core Web Vitals quantify how fast, responsive and stable a page feels to real users. Good scores improve conversions and are a Google ranking signal; poor scores frustrate visitors and can hold rankings back.
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For business owners
Slow, janky pages lose customers — every extra second of load time measurably increases abandonment. Core Web Vitals turn "the site feels slow" into three concrete numbers you can improve, and Google rewards good scores. Optimising them improves conversions and search visibility at the same time.
How it works (technical)
The three current vitals and their "good" thresholds:
- LCP (Largest Contentful Paint) — time until the largest visible element renders. Good: ≤ 2.5s.
- INP (Interaction to Next Paint) — responsiveness to user input across the visit. Good: ≤ 200ms.
- CLS (Cumulative Layout Shift) — how much the layout unexpectedly moves. Good: ≤ 0.1.
Measure with field data (Chrome UX Report) and lab tools (Lighthouse, PageSpeed Insights). Common fixes: optimise and preload the LCP image, reduce and defer JavaScript, and reserve space for images/ads to prevent shifts.
Real-world example
A publisher's articles scored poorly on CLS because ads inserted themselves after text loaded, pushing content down as readers tried to click. Reserving fixed space for each ad slot dropped CLS into the "good" range and cut accidental clicks and complaints.
Why it matters
Core Web Vitals affect both conversions and rankings. Scanners and page-experience checks measure them because they reflect what users actually feel.
How to fix it
Measure with PageSpeed Insights to get field and lab data.
Improve LCP: optimise/compress the hero image, preload it, and speed up server response.
Improve INP: reduce long JavaScript tasks, break up work and defer non-critical scripts.
Improve CLS: set width/height on images and reserve space for ads and embeds.
Re-measure with real-user (field) data over time, not just lab tests.
Best practices
Prioritise field data — it reflects real users on real devices.
Optimise the largest above-the-fold element first.
Always specify image dimensions to prevent layout shift.
Common mistakes
Optimising only lab scores while real users still suffer.
Loading heavy JavaScript that blocks interactivity.
Injecting content or ads without reserving space, causing shifts.
Frequently asked questions
Are Core Web Vitals a ranking factor?
Yes, as part of Google's page-experience signals. They rarely outweigh great content, but they can be a tie-breaker and they strongly affect conversions.
What replaced First Input Delay?
Interaction to Next Paint (INP) replaced FID in 2024 as the responsiveness metric, measuring latency across all interactions.
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