What you gain and what it costs
WebP encodes the same picture in fewer bytes than JPG, mostly by predicting blocks more cleverly. For a photograph at the same perceived quality the saving is roughly a third — enough to matter on a page with several images and enough to move a Largest Contentful Paint score.
The cost is one more generation of lossy compression. JPG threw detail away when it was made; WebP throws a little more away now. At quality 85 you will not see it. At 60, converted from a JPG that was already saved at 60, you might.
When not to bother
- The image is a logo, an icon or a screenshot — those belong in PNG or WebP lossless, and converting from JPG cannot undo the artefacts already there
- The file is going to someone who will open it in desktop software
- The original is under about 10 KB, where the format overhead dominates
The order that matters
Resize first, then convert. Converting a 4000-pixel photo to WebP and then scaling it down in the browser wastes most of the saving — the image resizer should run before this page does.
Questions
How much smaller will it get?+
Around 25–35% for a typical photograph at matching visual quality. The status line shows the real figure for your file rather than a promise — flat graphics and very small images save less, sometimes nothing.
Does converting lose quality?+
Slightly, and unavoidably. Your JPG is already lossy, so re-encoding it as lossy WebP is a second generation of loss. It is invisible at quality 85 for almost any photograph, but it is not free — always convert from the highest-quality original you still have.
Will WebP work everywhere?+
In every current browser, yes — Chrome, Firefox, Safari and Edge have supported it for years. Outside the browser is patchier: some older desktop software and a few email clients still refuse it. For the web it is safe; for a file someone will download and open, JPG is safer.