WebP vs JPG: photo format tradeoffs

Quality vs Size

According to Google's own published comparison, lossy WebP images are typically 25% to 34% smaller than comparable JPEG images at an equivalent SSIM (structural similarity) quality score. SSIM approximates how similar two images look to a human viewer rather than comparing raw file bytes, which is why the comparison is stated at 'equivalent quality' rather than at one fixed setting number. This means faster websites without necessarily sacrificing visual appeal, though actual savings vary by source image.

How each format compresses

JPEG splits an image into 8-by-8 pixel blocks, transforms each block with a discrete cosine transform (DCT), and discards higher-frequency detail a viewer is less likely to notice, typically after subsampling color information more aggressively than brightness. Lossy WebP is built on VP8's intra-frame video coding: it predicts each block from the blocks already decoded around it before applying a similar transform, so there is usually less error left to encode for the same visual quality — the main technical reason it tends to produce smaller files than JPEG at a comparable quality level.

Comparison Table

Where JPEG still has an edge

JPEG supports progressive rendering, where a browser can display a low-resolution preview of the full image immediately and sharpen it as more data arrives; WebP has no equivalent progressive mode in wide use. JPEG also remains the safer default for older photo-editing software, some print-production workflows, and any upload system that validates files against a fixed list of accepted formats that has not been updated to include WebP.

Pros and Cons

Generational loss on repeated re-saves

Both formats are lossy in their default photo mode, so both accumulate generational loss if you open a file, edit it, and re-export it as the same format repeatedly: each pass starts from pixels that already carry the previous pass's compression artifacts and discards a little more detail on top. Neither format's lossy mode is immune to this. If you expect to edit and re-export a photo more than once, keep a lossless master (a lossless WebP, a PNG, or the camera's original) and generate each lossy export from that master instead of re-compressing an already-compressed file.

Extensions and MIME types

JPEG files commonly use either the .jpg or .jpeg extension, a split that dates back to older filesystems limiting extensions to three characters; both point to the same format and MIME type, image/jpeg. WebP has a single standard extension, .webp, and its own MIME type, image/webp. When scripting a batch rename or a content-type check, accounting for both JPEG spellings is a common thing to miss.

When to Use Each

Choose WebP when the publishing workflow supports it and a smaller photo file matters more than absolute universal compatibility. Choose JPG when maximum compatibility with older software, devices, or print workflows matters more than file size.

Related guides

WebP vs PNG: format differences and use cases · What is WebP?

FAQ

Should I replace all JPGs with WebP?

Not automatically. Use WebP for modern web delivery when supported, and keep JPG fallbacks when compatibility matters.

Is WebP lossless?

WebP supports both modes. Lossless WebP preserves pixel data exactly, similar to PNG. Lossy WebP, the default for photos, behaves more like JPEG, trading some quality for smaller files.

Is WebP smaller than JPEG?

Usually. WebP lossy images are typically 25% to 34% smaller than comparable JPEG images at a similar visual quality level, per Google's published comparison, though exact savings depend on the source image.

Does WebP support progressive loading like JPEG?

No, not in the way JPEG's progressive mode works. A browser showing a WebP image generally waits for enough of the file before rendering it, rather than sharpening a low-resolution preview as more data streams in.

Will every photo editor or upload form accept WebP?

Not always. Some older editing software and some upload forms only accept a fixed list of formats that has not been updated to include WebP. JPEG remains the safer default when you do not control the receiving system.

Does re-saving a photo repeatedly degrade it further?

Yes, for both formats, if you keep re-exporting in the same lossy mode. Each re-encode works from pixels that already carry the previous pass's compression artifacts, so detail keeps degrading a little each time. Keep a lossless master and export a fresh lossy copy from it rather than repeatedly re-saving the same lossy file.