What are Core Web Vitals and why should I care?

Three metrics Google uses to measure page experience: Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). I tested improvements across 50 client sites between January and November 2024. Sites that passed all three metrics saw an average 12% increase in organic traffic within 90 days.

Which metric had the biggest impact?

LCP improvements showed the clearest correlation with ranking changes. I focused on images first - converting to WebP, adding dimensions, lazy loading below the fold. One e-commerce site dropped LCP from 4.2s to 1.8s by moving hero image CSS inline and preloading the banner. Traffic increased 18% in two months.

What about CLS fixes?

CLS was trickier. Reserve space for ads, set image and video dimensions, avoid inserting content above existing content. A news site had 0.42 CLS from ad injections. Added min-height containers for ad slots, dropped to 0.08. Bounce rate fell 23%.

How long until results show up?

Most sites showed measurable changes between 4-8 weeks. Google needs time to recrawl and reassess. I tracked daily in Search Console and saw gradual improvements, not overnight jumps.

What if my scores are already passing?

Field data matters more than lab data. Check the Chrome User Experience Report for real user metrics. One site passed in PageSpeed Insights but failed in CrUX because mobile users on slow connections struggled. Fixed by reducing JavaScript from 890KB to 340KB.

Worth the effort for small sites?

Yes, especially if competing against larger sites. Smaller sites can move faster. One local service site with 200 pages beat national competitors by fixing Core Web Vitals in three days.