Core Web Vitals and Page Speed: How Do They Affect Rankings?

Short answer: Core Web Vitals are three numbers with clear thresholds. LCP (time until the main content renders) should be under 2.5 seconds; INP (response to interaction) under 200 milliseconds; CLS (layout shift) under 0.1. Measure in two layers: Lighthouse/PageSpeed lab results give direction, but Google ranks on real-user data (CrUX) — check both. We lived this on our own site this week: our lab LCP was 7.9 seconds; two fixes — giving the hero image loading priority and deferring tracking scripts until after page load — brought it to 3.2 seconds the same night. The three highest-return fixes are nearly universal: compress and right-size images, remove or defer unused JavaScript, and prioritize the hero image while lazy-loading the rest. Measure mobile first; that's where Google and your customers are.

Core Web Vitals are the three core metrics Google uses to measure user experience: loading speed (LCP), interaction responsiveness (INP) and visual stability (CLS). Weak values lower both rankings and conversions, because users don't wait on a slow page.

The three metrics

How to improve

Look at field data

Lab tests (e.g. Lighthouse) give direction, but field data (CrUX / Search Console) shows the real user experience.

Especially on bot-protected sites, synthetic tests can mislead; make decisions with real user data.

A caution about the numbers: speed scores also get misused as a sales weapon — not everyone shouting 'you're under 50, disaster!' is right. The honest reading: under 50 genuinely loses customers; 50-89 means speed has earned a place in your fix queue; above 90, the same effort usually earns more when spent on content. It's not the score itself but the LCP seconds and their source — image or script — that set your action plan.