Reasons to convert PNG to JPG, and they are mostly about weight
A PNG describes every pixel exactly. That is the right choice for a logo, a screenshot or anything with sharp edges, and the wrong one for a photograph, where being exact costs an enormous amount of space for detail nobody can see. A camera photo saved as PNG routinely runs 8 to 15 MB. The same photo as a good-quality JPEG is under a megabyte and looks the same at any normal viewing size.
So the honest rule is about content, not preference. Photographs and photographic renders belong in JPEG. Text, line art, UI screenshots, charts and flat-colour illustrations belong in PNG, and converting them to JPG will make them look worse while saving less than you expect.
Transparency has to go somewhere
JPEG has no alpha channel. None. So before the encoder ever runs, every transparent pixel in your PNG must be painted with something opaque.
That is a decision, and this page hands it to you rather than making it quietly. The default is white, which is what most people want most of the time. If your image is destined for a dark page, set a dark colour here instead. Doing it now avoids the classic result: a product shot with a crisp cut-out edge that arrives with a white fringe glowing around it.
Semi-transparent pixels blend against the colour you choose, so soft shadows and anti-aliased edges come out clean rather than as a hard fringe.
Picking a quality level
The default is 92 percent, which is high enough that side-by-side comparison is difficult on photographic content. Dropping to 85 is usually still invisible and saves a further 30 percent or so. Below 80 you begin to see the 8 by 8 block structure the codec works in, first around high-contrast edges.
Going the other way is mostly wasted. From 95 to 100 the file can double while the visible difference stays near zero, because at that point the encoder is faithfully preserving noise.
JPG and JPEG are the same thing
Worth clearing up, because it a search for png to jpeg and a search for png to jpg want the same output. The
three-letter extension is a leftover from the era when filenames allowed only
three characters after the dot. There is no format difference, no quality
difference and no compatibility difference: .jpg and .jpeg are byte-for-byte
the same kind of file.
Everything stays on your device
Files are read, decoded, re-encoded and handed back inside the browser tab. No upload step exists in this tool, which also means large batches are limited only by your own memory and patience rather than by someone else's queue.