WebP vs AVIF: WebP is smaller and faster to encode than JPEG (Google’s own study found it 25-34% smaller at equivalent SSIM quality) and has near-universal modern browser support, while AVIF compresses even further — up to 50% smaller than WebP in some cases — but encodes more slowly and still has narrower support in older browsers and some image tools. For most tech blogs, WebP with a JPEG/PNG fallback is the safer default; AVIF is worth adopting for the largest hero images once your CDN and CMS pipeline can generate it reliably.
In this guide:
What each format actually does
Both formats exist to solve the same problem: JPEG and PNG are decades old and leave real file-size savings on the table. WebP, developed by Google and released in 2010, uses prediction-based compression derived from the VP8 video codec. AVIF, standardized more recently, is based on the AV1 video codec and takes advantage of a newer generation of compression techniques. In the WebP vs AVIF comparison, AVIF is the younger, more advanced format on paper — but “more advanced” doesn’t automatically mean “the right choice for your site today,” which is why the practical differences below matter more than the codec generation.
Compression: the WebP vs AVIF numbers
Google’s own developer documentation states that WebP lossy images are “25-34% smaller than comparable JPEG images at equivalent SSIM quality index,” which is a meaningful reduction on a page with dozens of product or article images. AVIF pushes further: independent and vendor testing has shown AVIF files running up to 50% smaller than the equivalent WebP file at similar perceived quality, particularly on photographic images with lots of detail and gradients. The gap narrows on simpler images like screenshots or line-art graphics, where WebP’s savings over the original JPEG or PNG are already large and AVIF’s additional gain is smaller in absolute terms. If your site is mostly photography or complex imagery, AVIF’s compression advantage is worth chasing; if it’s mostly diagrams and screenshots, WebP alone may already get you most of the available savings.
Browser and tool support
WebP support is effectively universal at this point across Chrome, Firefox, Safari, and Edge, and has been for several years, which is why most image-optimization plugins default to it. AVIF support is broader than it used to be but still has gaps: some older browser versions, some email clients, and a number of image-editing and CMS tools either can’t decode AVIF at all or handle it inconsistently. This matters practically — if your workflow involves designers opening exported images in older desktop software, or if a meaningful share of your traffic comes from browsers that don’t fully support AVIF, you need a fallback chain (AVIF, then WebP, then JPEG/PNG) rather than serving AVIF alone. The HTML `
Animation and transparency
Both formats support transparency (alpha channel) and animation, unlike JPEG, which supports neither. WebP’s animation support has been in production use for longer and is more consistently implemented across the tools that generate and serve animated images, making it a practical GIF replacement today. AVIF also supports animation, but tooling for creating animated AVIF files is less mature than for WebP, and file-size gains for animated content specifically are less dramatic than the static-image comparisons usually cited. If replacing animated GIFs is a priority, WebP is currently the more dependable choice; AVIF’s animation capability is more of a “will be useful later” feature than a “ready now” one for most teams.
Encoding time and CPU cost
This is the tradeoff most comparisons skip. AVIF’s smaller output files come at the cost of significantly longer encoding time — often several times longer than WebP at equivalent settings, because AV1-based encoding does more computational work per image to find those extra savings. On a site that generates thousands of image variants (multiple sizes and formats per uploaded photo, which most responsive-image setups require), that encoding cost adds up in build time or server CPU, particularly if images are encoded on-demand rather than pre-generated. Sites using a CDN or image service that handles format conversion at the edge avoid this cost directly, but it’s still worth knowing before committing to AVIF as your primary format for a high-volume image library.
What this means for SEO and Core Web Vitals
Neither format directly affects search rankings the way page speed does — Google’s guidance treats image format as one input into Largest Contentful Paint and overall page weight, not a ranking factor by itself. Smaller image files reduce LCP time for image-heavy pages, which is where the WebP vs AVIF choice actually shows up in Core Web Vitals reports. In practice, moving from unoptimized JPEG/PNG to WebP typically produces the largest single jump in image-related LCP improvement, since it’s the easier migration with universal support. The additional gain from WebP to AVIF is real but smaller in most Core Web Vitals reports, since you’re optimizing an already-optimized baseline rather than starting from raw JPEGs.
Our recommendation
Serve WebP as your default modern format today, with a JPEG or PNG fallback for any remaining older browsers or tools in your pipeline — this alone captures most of the available performance win with minimal compatibility risk. Layer AVIF on top for your largest, most visually complex images (hero banners, full-width photography) where the extra compression is worth the additional encoding cost, using a `
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