Core Web Vitals and site speed

Core Web Vitals are three metrics that describe how a page feels to real visitors. Google's ranking systems use them, and they also affect conversions, often more than rankings.

The three metrics

Metric	Measures	Good	Poor
LCP, Largest Contentful Paint	When the main content (usually a hero image or heading) has loaded	≤ 2.5 s	> 4 s
INP, Interaction to Next Paint	How quickly the page responds to taps, clicks and key presses	≤ 200 ms	> 500 ms
CLS, Cumulative Layout Shift	How much the layout jumps while loading	≤ 0.1	> 0.25

Field data and lab data

• Field data comes from real Chrome users through the Chrome UX Report (CrUX), over a rolling 28 days. The Search Console Core Web Vitals report and the top of PageSpeed Insights use it. Pages with too little traffic have no field data of their own, so Search Console may fall back to grouped or origin-level data, or show nothing.
• Lab data comes from a simulated load in Lighthouse, on one simulated device and network. It varies from run to run. Use it to debug, not to judge.

The Search Console report groups similar URLs together, and a group's status is its worst metric.

Where speed matters for ranking

The fixes that matter most

LCP (loading)

• Do not lazy-load the main above-the-fold image. Consider fetchpriority="high" on it.
• Serve images at the size they are displayed, in WebP or AVIF.
• Reduce server response time with caching, a closer server or a CDN, and fewer slow database queries.
• Remove render-blocking CSS and JavaScript where possible.

INP (responsiveness)

• Reduce heavy JavaScript: unused libraries, large third-party scripts, chat widgets and tag managers loading everything.
• Break long tasks into smaller ones, and defer non-essential work.
• Be careful with scripts that run on every interaction.

CLS (stability)

• Set width and height or aspect-ratio on images, videos and embeds.
• Reserve space for ads, cookie banners and dynamic content, or show them without pushing content down.
• Load web fonts in a way that avoids large layout jumps.

Platform notes

• PrestaShop: enable the built-in CCC options (combine, compress and cache) in Advanced Parameters, then Performance, and test the result, because some modules break. Disable unused modules, and check that image sizes match the theme.
• WordPress / WooCommerce: use a caching plugin, and audit heavy plugins and page builders, which often cause poor INP.
• Shopify: theme choice and installed apps make the biggest difference. Remove apps you do not use, because many inject scripts.