Both formats are lossy, both are supported by current browsers, and for most photographs both will look identical at the same file size. The differences that matter are elsewhere.
Where WebP wins
- File size. At matched visible quality, a WebP is usually smaller than the JPEG for the same image. How much depends entirely on the image.
- Transparency. WebP stores an alpha channel. JPEG cannot store transparency at all, so a logo with a transparent background has to become PNG or stay WebP.
- Every current browser reads it. The compatibility argument against WebP is out of date for web use.
Where JPG wins
- Everything that is not a browser. Word documents, older desktop software, print workflows, some email clients and a long tail of other tools open a JPG without thinking and may refuse a WebP outright.
- Predictability. JPEG is the format every tool has been tested against for decades.
The rule that covers most cases
If the file is going onto a web page, WebP is usually the better choice: smaller file, same appearance, and it keeps transparency. If the file is going to a person, a form, an email attachment or a print shop, JPEG is the safer choice, because the next program to open it is unknown.
When in doubt, send the JPEG. A file that opens is worth more than a file that is smaller.
What about PNG?
Keep PNG for screenshots, diagrams and anything with sharp text or flat colour, where lossless storage is worth the size. Do not keep photographs as PNG - it is several times larger for no visible gain. Why is my PNG file so large goes through the reasoning.
Trying both takes a minute
The most reliable answer comes from compressing the same image twice and comparing. The compressor offers all three formats, shows the real size of each result, and never uploads anything, so trying is free and instant.
Compress to WebP or compress to JPG, then keep whichever is smaller and looks right at the size you will actually use.