Best image format for SEO.

Format comparison for SEO

Why image format matters for SEO

Google has repeatedly confirmed that page speed is a ranking factor. Images make up the majority of bytes on a typical web page — and the format you choose determines how many of those bytes are actually necessary. A WebP image can be 35% smaller than JPEG at the same visual quality, and an AVIF image can be 50% smaller. That difference translates directly into faster load times, better Largest Contentful Paint (LCP) scores, and higher organic rankings. Choosing the wrong format means you are serving megabytes of unnecessary data to every visitor.

JPEG and SEO

JPEG has been the default image format on the web for decades. Its universal browser support (100%) makes it a safe fallback for any SEO strategy. However, JPEG's lossy compression is less efficient than modern alternatives. A high-quality JPEG is typically 25-35% larger than an equivalent WebP. If your site still relies entirely on JPEG, you are leaving significant page speed improvements on the table. Use our JPEG compressor to optimise your existing JPEGs with mozJPEG encoding, but consider serving WebP or AVIF alongside JPEG for modern browsers.

WebP — Google's recommended format

WebP was created by Google specifically for the web. It supports both lossy and lossless compression with alpha transparency and animation. Google recommends WebP as the default image format for modern websites, and tools like PageSpeed Insights and Lighthouse explicitly flag JPEGs and PNGs that should be served as WebP. With 97% browser coverage, WebP is safe to use as your primary format with a JPEG fallback.

The SEO benefit is straightforward: WebP images load faster, improving LCP, First Contentful Paint (FCP), and overall page speed — all of which are Google ranking signals. Our WebP compressor lets you convert and optimise images to WebP with fine-grained quality control. For bulk conversion, the bulk compressor handles entire folders at once.

AVIF — the performance leader

AVIF delivers the best compression efficiency of any widely supported image format. Based on the AV1 video codec, it achieves roughly 50% smaller files than JPEG at the same quality. For SEO, this means dramatically smaller LCP images and faster page loads. AVIF also supports HDR, wide colour gamut, and lossless compression. Browser coverage is around 90% — growing quickly — and it is supported in all major browsers except some older Safari versions. Serve AVIF with a WebP or JPEG fallback using the <picture> element. Our AVIF compressor supports full-quality control and batch processing.

PNG for specific use cases

PNG is lossless and supports full alpha transparency, making it essential for logos, icons, and images with sharp edges or text overlays. However, PNG files are typically 5-10x larger than equivalent JPEGs for photographic content, which makes them a poor choice for SEO-focused image optimisation. Use PNG only when you need transparency or pixel-perfect reproduction. Our PNG compressor reduces PNG size by 10-40% with lossless optimisation or up to 70% with lossy colour quantization.

How image compression improves Core Web Vitals

Largest Contentful Paint (LCP) measures how long the largest visible element takes to render. On most pages, that element is an image. Switching from JPEG to WebP can cut your LCP images from 400 KB to 260 KB — a 35% reduction. Switching to AVIF can cut them to 200 KB. Lower LCP scores are directly correlated with higher search rankings, especially for mobile results where connection speeds are variable.

Beyond LCP, smaller images reduce Total Blocking Time (TBT) by freeing up the main thread sooner, and lower Cumulative Layout Shift (CLS) when image dimensions are properly set. The bulk image compressor processes hundreds of images in parallel with automatic format conversion, making it easy to optimise your entire media library for Core Web Vitals.

The verdict

For the best balance of browser support, file size reduction, and SEO impact, use WebP as your primary format with a JPEG fallback. For maximum performance gains, serve AVIF with WebP and JPEG fallbacks using the <picture> element. Reserve PNG for images that genuinely need transparency or lossless quality. For a deeper dive into specific format comparisons, read our WebP vs AVIF comparison and best image format for websites guides.