Optimize Images for Core Web Vitals: LCP & CLS Guide

·6 min read
Core Web VitalsLCPPerformance
Alex Chen· Image Performance Engineer

Core Web Vitals and Images

Images directly affect two of three Core Web Vitals:

  • LCP (Largest Contentful Paint): The hero image is usually the LCP element
  • CLS (Cumulative Layout Shift): Images without dimensions cause layout shifts

    • Fixing LCP

  • Optimize the hero image: Convert to WebP/AVIF, compress to quality 80
  • Preload the LCP image:
  • Use responsive images with srcset to serve appropriate sizes
  • Target: LCP image under 100KB, loading in under 2.5 seconds

    • Fixing CLS

  • Always set width and height attributes on tags
  • Use aspect-ratio CSS for responsive images
  • Reserve space for images that load lazily

    • Impact on SEO

    Google uses Core Web Vitals as ranking signals. A 1-second LCP improvement can increase organic traffic by 5-10%.

    Related Guides

  • Image Optimization for Next.js
  • Reduce Image File Size for Website

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