A photograph saved as PNG is typically five to ten times larger than the same picture as a JPG, for no visible benefit. Converting is usually the single biggest saving available. One thing to know first: JPG cannot store transparency.
Output preset to JPG. Transparent areas will be flattened.
PNG stores every pixel exactly. That is precisely what you want for a logo with hard edges, and precisely what you do not want for a photograph.
In a photograph almost every pixel differs slightly from its neighbour — sensor noise, texture, subtle gradients in a sky. PNG faithfully records all of it, including the parts no human could ever perceive. JPEG discards exactly that imperceptible layer, which is why the same image can be a tenth of the size and look identical.
A screenshot of a document is a good PNG. A photograph of a document is a bad one.
JPG has no alpha channel. It cannot store transparency at all.
When a PNG with transparent areas is converted to JPG, those areas have to become something. They are filled — typically with white or black — and the transparency is gone permanently. For a photograph this is irrelevant, because there was none. For a logo meant to sit over a coloured background, it ruins the file.
If your image needs transparency and you want it smaller, convert to WebP instead. WebP supports an alpha channel and is still far smaller than PNG.
Convert to JPG: photographs saved as PNG, screenshots of photographic content, anything with no transparency where the file is uncomfortably large.
Keep as PNG: logos, icons, anything with transparency, screenshots containing small text, diagrams, line art, and any file that will be edited again. JPEG blurs sharp edges and text in a way that is immediately obvious and cannot be undone.
A quick test: if you zoom in and see hard-edged shapes or text, keep PNG. If you see continuous tone and texture, convert.
For a genuine photograph, expect the JPG to be somewhere between a fifth and a tenth of the PNG. A 4MB PNG photograph commonly lands between 300KB and 700KB as a good-quality JPG with no perceptible difference on screen.
For graphics the saving is much smaller and sometimes negative — JPEG is bad at flat colour and can produce a larger file than PNG while also looking worse. If the result comes back barely smaller, that is the format telling you the image should stay a PNG.
Drop the PNG in above and press Compress — the output format is already set to JPG. Everything runs in your browser, so the file is never uploaded.
Yes. JPG has no alpha channel, so transparent areas are filled with a solid colour. If you need to keep transparency and reduce file size, convert to WebP instead.
For photographs, typically five to ten times smaller with no visible difference. For logos, icons and flat graphics the saving is far smaller and the result can look worse — those should stay as PNG.
WebP is smaller than both and keeps transparency, making it the better choice for websites. Convert to JPG when the file is going somewhere that expects a universally supported format.