Image Optimisation for Core Web Vitals: 2026 Guide

Core Web Vitals (CWV) are Google's signals for user experience and page performance. Images are often the biggest bottleneck. Optimizing images can transform your CWV scores and rankings.

The Three Core Web Vitals

Largest Contentful Paint (LCP): How fast the main content loads. Cumulative Layout Shift (CLS): Visual stability. First Input Delay (FID): Interactivity. Images affect all three.

Image Size and LCP

Large unoptimized images delay LCP. Converting JPEG to WebP or AVIF reduces file size by 25–50%, dramatically improving LCP scores.

Lazy Loading and LCP

Load images only when they enter the viewport using native lazy loading (loading="lazy"). This defers image downloads and speeds up initial page load.

Responsive Images

Serve different image sizes to different devices using srcset and sizes. A mobile device should never download a 4K desktop image.

Format Choice

Use WebP or AVIF for photographs. Use PNG for graphics. Use SVG for icons. Each format is optimized for its content type.

Optimization Workflow

1. Convert all images to modern formats (WebP/AVIF) with QuickConvert.
2. Resize for each breakpoint (mobile, tablet, desktop).
3. Implement lazy loading and responsive markup.
4. Monitor CWV scores in Google Search Console.