When converting PNG to JPG is the right call
PNG and JPG solve different problems, and converting between them is only worth doing when the destination genuinely suits your image. JPG is built for photographs and any picture with smooth gradients and continuous tone. For that kind of content it produces files a fraction of the size of the equivalent PNG, which is why converting a photographic PNG to JPG so often cuts the file by 70 to 90 percent with no visible difference at normal viewing sizes.
Where it goes wrong is with graphics that PNG was designed for: logos, screenshots with text, line art, anything with hard edges and flat colour. JPG compresses those by smearing detail across blocks, so sharp edges pick up a faint halo and small text softens. If your PNG is a screenshot or a diagram, converting it to JPG will make it look slightly worse for a smaller saving than a photo would give. In that case, keeping the PNG or converting to WebP is the better move.
What happens to transparency
PNG can store transparency; JPG cannot. Every JPG pixel is fully opaque, so when a transparent PNG is converted, something has to be decided for the see-through areas. A careless converter leaves them black, which is why people are surprised to find a logo they converted now sits on a dark rectangle.
This tool flattens transparency onto solid white instead, because white is what most pages, documents and print backgrounds expect. The result looks right in the overwhelming majority of cases. If your image needs to stay transparent — a logo to drop onto a coloured background, a cut-out product shot — then JPG is simply the wrong target, and you should convert to WebP or keep the PNG, both of which preserve the alpha channel.
Everything happens in your browser
The conversion runs entirely on your own device using the browser's built-in image handling. Your PNG is decoded, painted onto a canvas, and re-encoded as a JPG without a single byte being sent to a server. That matters for anything sensitive — a scanned document, an ID, an unreleased design — because a file that never leaves your machine cannot be logged, cached or leaked by a service in the middle.
It also means the tool is fast and works offline once the page has loaded, and it can handle a batch: drop a folder of PNGs and each is converted in turn, with the size saving shown per file and a single ZIP download at the end. There is no queue, no account and no upload limit beyond what your own device can hold in memory.
Choosing the quality that fits
Because JPG is lossy, it gives you a quality control, and where you set it is a genuine trade-off between file size and fidelity. Push it low and the file shrinks but detail smears; push it high and the JPG approaches the original at the cost of size. The default is tuned so that ordinary photographs look untouched.
In practice, leave it at the default for sharing and uploads, raise it toward the top only for images you will print or crop into later, and drop it when you specifically need the smallest possible file. The conversion is immediate and runs on your device, so trying a value and checking the result costs nothing but a glance.