Core Web Vitals are three metrics defined by Google to objectively measure the user experience of a web page: loading speed, responsiveness to interaction, and visual stability. Since 2021 they have been an official part of Google's ranking signals — a small but real factor.
What are Core Web Vitals?
The three metrics are:
- LCP (Largest Contentful Paint): How long it takes for the largest visual element on the page to appear.
- INP (Interaction to Next Paint): How long it takes for the page to respond to a user's click/tap.
- CLS (Cumulative Layout Shift): How much elements unexpectedly shift position while the page loads.
All three are calculated from real user data (anonymous telemetry from Chrome users); they reflect the real experience of real visitors, not lab tests.
LCP — Largest Contentful Paint
LCP is the moment the user feels "the page has loaded" — usually a hero image, a heading block, or a large video thumbnail. Google's thresholds:
| Value | Rating |
|---|---|
| 2.5 seconds or less | Good |
| 2.5 – 4 seconds | Needs improvement |
| More than 4 seconds | Poor |
The most common causes: large unoptimized images, slow server response time, render-blocking CSS/JS files, and late-loading fonts.
INP — Interaction to Next Paint
INP, which replaced the older FID (First Input Delay) metric in 2024, measures the responsiveness of all interactions on the page, not just the first one. It captures whether the screen freezes when you press a button.
| Value | Rating |
|---|---|
| 200 milliseconds or less | Good |
| 200 – 500 ms | Needs improvement |
| More than 500 ms | Poor |
The most common cause is heavy JavaScript execution that keeps the main thread busy for long periods — third-party scripts running during page load (ads, live chat, analytics tools) are frequent culprits.
CLS — Cumulative Layout Shift
You're about to click a news story when the page suddenly shifts and you accidentally click an ad — that is exactly what CLS measures. Images without defined dimensions, late-loading ad/banner slots, and late-loading fonts (font swap) are the most common causes.
| Value | Rating |
|---|---|
| 0.1 or less | Good |
| 0.1 – 0.25 | Needs improvement |
| More than 0.25 | Poor |
How do they really affect SEO?
It's important to set the right expectations here: Core Web Vitals are not as strong a ranking factor as content quality and search intent match. According to Google itself, they act as a tiebreaker "between two equally good pieces of content" — in other words, strong Web Vitals scores won't save weak content, but between two pages of similar quality, the faster one may come out ahead.
Their indirect impact, however, is greater than their direct impact: a slow, unstable page drives users away, increases bounce rate, and reduces session duration — and these behavioral signals affect rankings far more strongly than Core Web Vitals.
How are they measured?
- PageSpeed Insights: Shows both real user data (if available) and lab test results on a single screen. The most practical starting point.
- Search Console → Core Web Vitals: Groups all pages of your site and shows at a glance which are "good", "need improvement", or "poor".
- Chrome DevTools → Lighthouse: Provides an instant, detailed analysis in the developer console.
Practical steps for improvement
- Convert images to modern formats. Use WebP/AVIF, compress them at their actual display
size, and defer below-the-fold images with
loading="lazy". - Set fixed dimensions for images and ad slots. Let the browser know how much space to reserve before content loads — this directly improves CLS.
- Reduce render-blocking resources. Load non-critical CSS/JS files deferred (defer/async).
- Optimize fonts. Use
font-display: swap, and don't load unnecessary weights/characters. - Limit third-party scripts. Every live chat, analytics, or ad script you add can worsen INP; keep only the ones you truly need.
- Reduce server response time. Caching and a good hosting choice are the most overlooked yet most effective inputs to LCP.
Order of priority: The biggest gains usually come from images — on most sites, the source of the LCP problem is a single large unoptimized image. Fix that first, then move on to the other items.
If you still can't attract visitors even with good page speed, the bottleneck is visibility — in that case, check out our CTR improvement guide or our general article on increasing organic traffic.