How does WebP compression work?
WebP has two modes. Lossy WebP comes from the VP8 video codec: it predicts each block of pixels from its neighbors, stores only the difference, and smooths block edges with a filter, which is why it shows fewer blocky artifacts than JPEG at the same size. Lossless WebP keeps every pixel exactly and is designed for graphics. Both modes can carry transparency.
The quality slider controls lossy WebP. Big savings usually come from files that were exported in lossless mode or at quality 90–100, often by design tools or by converters left on their maximum setting: a photo stored as lossless WebP can be several times larger than the same photo at quality 78, with no difference you would notice on a web page.
What WebP quality should I use?
WebP quality ranges and where each one fits.
| Quality | Use it for | Notes |
|---|---|---|
| 90–100 | Graphics with fine text, assets you will edit again | Large files; little saving over the original |
| 80–88 | Screenshots, interface images, banners with text | Keeps text edges clean |
| 75–80 (78 here) | Photos in articles, product images | No visible loss on most photos |
| 60–70 | Thumbnails, backgrounds behind text | Slight softening, rarely noticed at small sizes |
| Below 50 | Only to meet a strict size cap | Smearing and blotchy color |
These ranges match what most sites settle on after testing. The reasoning behind each one, with examples, is in the best WebP quality setting.
Why is my WebP file so large?
- It was saved as lossless. Lossless suits logos and flat graphics, not photos. Re-encoding a lossless photo at 78 is where the biggest savings are.
- It was saved at quality 95–100. The last few quality points cost a lot of bytes and add detail that no screen shows.
- Its dimensions are far larger than needed. A 4000 px photo shown in an 800 px column carries 25 times the pixels it needs. Use Limit width.
- It is animated. The compressor is made for still images; keep animated WebP files as they are.
Why didn't my WebP get smaller?
Many websites, CMS plugins and CDNs already serve WebP at quality 75–80. Re-encoding such a file at 78 has nothing left to remove and would only add a second round of loss, so the tool keeps the original. To shrink it further, lower the quality to 65–70 or reduce the width. If you are not sure which images on a page are worth the effort, the free image audit lists how much each one would save.
When should you use a different format?
WebP is the right choice for web pages, but some upload forms, email clients and older desktop software still refuse it. In that case set the output format to JPG for photos or PNG for graphics, and the compressor converts as it compresses. Going the other way, if your source is a JPG or PNG and you want WebP for your site, use JPG to WebP or PNG to WebP. For newer formats, WebP vs AVIF explains when AVIF is worth it.