How JPEG compression works
JPEG divides an image into 8×8 pixel blocks and applies a Discrete Cosine Transform (DCT) to each block. The DCT converts the pixel values into frequency components — essentially describing the block in terms of how much low-frequency (smooth) and high-frequency (detailed) information it contains. The quantization step then rounds off the high-frequency components, which is where the lossy part happens. The degree of rounding is what the quality slider controls.
The fixed 8×8 block size is JPEG's main limitation. Compression decisions cannot account for patterns that span a larger area, and the block boundaries become visible as artifacts (the characteristic blocky look of a low-quality JPEG) when aggressive compression is applied.
How WebP compression works
WebP's lossy mode is based on VP8, a video codec developed for web video. It uses a macroblock prediction model: before encoding each region, the encoder predicts what those pixels look like based on surrounding already-encoded regions, then only encodes the difference (residual). If the prediction is accurate, the residual is small and compresses efficiently.
VP8 also uses larger block sizes — up to 16×16 pixels — which allows it to model larger smooth areas more efficiently and reduces boundary artifacts. The result is better quality at equivalent file size, particularly in smooth gradient areas like sky, skin tones, and out-of-focus backgrounds.
WebP also applies entropy coding (arithmetic coding) that is more efficient than JPEG's Huffman coding for the final compressed bitstream. This contributes additional size savings independent of the prediction model.
The practical size difference
For photographs and complex imagery, WebP is typically 25–35% smaller than JPEG at equivalent perceived quality. For some content types — especially images with large smooth areas — the difference can be 40% or more. For very detailed, noisy content like macro photography or grain-heavy images, the advantage narrows.
WebP also supports lossless compression (for pixel-accurate output) and alpha transparency (for images with transparent areas). Lossless WebP is often smaller than PNG for images with complex, varied content, though PNG can win on very simple flat-color graphics.
WebP or JPG: a quick decision
WebP works in every modern browser — roughly 97% of global usage — so for the web itself it is rarely the wrong choice. The exceptions are mostly off-web, where older or specialized software still expects JPEG.
| Context | Use | Why |
|---|---|---|
| Website and app images | WebP | 25-35% smaller, supported by ~97% of browsers |
| Email campaigns | JPG | Most email clients do not render WebP |
| Print delivery | JPG or TIFF | WebP is a web-only format |
| Stock sites and marketplaces | JPG or PNG | Many still require legacy formats |
| Maximum compression | AVIF | About 30-50% smaller than WebP |
When WebP is not the right choice
Despite its technical advantages, WebP has real limitations:
- Email clients: Most major email clients — Apple Mail, Outlook, Gmail desktop — do not support WebP. If an image needs to appear in email HTML, use JPEG or PNG. WebP in an email will display as a broken image for a significant portion of recipients.
- Some native apps and SDKs: If images will be consumed by a mobile app, an API response, or a third-party integration, verify WebP support before using it. Libraries and SDKs may not have WebP decoders.
- Older CMS plugins and image editors: Some older versions of WordPress plugins, Photoshop, Lightroom, and Figma have limited or no WebP support. Check your toolchain.
- Print workflows: Print service providers typically expect JPEG, TIFF, or PDF. WebP is a web format and is not appropriate for print delivery.
- Maximum compression priority: If file size is the overriding concern and encoding speed is not a constraint, AVIF typically outperforms WebP by 30–50% at equivalent quality.
WebP versus AVIF: knowing when to push further
AVIF is newer and achieves better compression than WebP for most content types. If you are building a new project in 2026 with a modern audience, AVIF with a WebP fallback (using the
Converting JPEG to WebP
PhotoTools converts JPEG and PNG files to WebP in your browser without uploading anything to a server. Drop in your images, choose WebP as the output format, and use the quality slider to find the right size-to-quality balance. For most photographs, quality 78–82 in WebP produces output that is visually indistinguishable from the source JPEG at normal viewing sizes while being significantly smaller.
Compare the converted file at the display size rather than at 100% zoom. Differences that look significant when zoomed in to individual pixels are often invisible at the actual rendered width on a web page.