Export dialogs ask the same question every time: PNG, JPG or WebP? The rule is short, and most of this page is the evidence for it. I ran the three conversions people search for through the image format converter on this site and wrote down what came out. Two of the three results are the opposite of what most people expect.
The short answer
| What you have | Save it as | Why |
|---|---|---|
| A photograph | JPG, or WebP on your own site | Small files; no transparency needed |
| A logo, icon, screenshot or diagram | PNG | Edges and text stay sharp |
| Anything with a transparent background | PNG or WebP | JPG cannot store transparency |
| Images on a website you control | WebP | Smaller than both at the same quality |
| A file someone else must open anywhere | JPG for photos, PNG for graphics | Opens in everything, including old software |
If you remember one line: photos to JPG, graphics to PNG, your own website to WebP.
The one idea behind every trade-off
JPG and WebP are lossy. They shrink a file by throwing away detail the eye is unlikely to miss, and the quality setting decides how much. Between 80 and 90 a photo looks the same; push lower and colours band, edges smear and blocky squares appear around fine detail. PNG is lossless: every pixel is stored exactly, so a screenshot or a logo stays crisp through a hundred saves, and a photograph with millions of slightly different pixels becomes enormous.
That is the whole explanation for the three measurements below.
Three conversions, measured
All three ran in the browser, in the converter on this site, with its default settings: quality 90 and white as the fill colour for transparent areas. Nothing was uploaded; the tool redraws the image on a canvas and re-encodes it on your device.
JPG to PNG: 63.9 KB became 540.3 KB. A 63.9 KB photo came out as a 540.3 KB PNG, more than eight times the size, and it gained no detail at all. PNG is lossless from the moment you save it; it cannot put back what JPG compression already removed. The one real gain is that later edits can be saved without another round of JPG loss. Convert to PNG because a system demands it or because you are about to add transparency in an editor, not because the format sounds higher quality.
| File | Format | Size |
|---|---|---|
| Original | JPG | 63.9 KB |
| Result | PNG | 540.3 KB |
PNG to JPG: 1.4 KB became 3.0 KB, and the transparency became white. The source was a 400 × 240 drawing with a coloured rectangle on a transparent background. The JPG was twice the size. Flat areas of one colour compress extremely well as PNG, and JPG has nothing to gain on them; its advantage is photographs. The transparent area was filled with white, because JPG has no transparency at all, and no setting changes that. The converter lets you choose the fill colour, so match it to wherever the JPG will sit; if the image has to float over other content, stay on PNG or WebP.
| PNG original | JPG result | |
|---|---|---|
| Size | 1.4 KB | 3.0 KB |
| Transparency | yes | none, filled white |
| Dimensions | 400 × 240 | 400 × 240 |
WebP to JPG: 15.6 KB became 47.9 KB. A 1,200-pixel-wide WebP from this blog's image library came out as a JPG three times its size at quality 90. WebP's compression does not carry over; the browser decodes the image to pixels and encodes a fresh JPG. Convert to JPG when a form or an old program refuses WebP, not to save space.
| WebP original | JPG result | |
|---|---|---|
| Size | 15.6 KB | 47.9 KB |
| Quality setting | — | 90 |
| Dimensions | unchanged | unchanged |
The pattern: changing the format is not compression. Two of the three conversions made the file larger. When the goal is a smaller file, run the format you already have through the image compressor; compressing an image to 100 KB shows what that looks like on a real photo.
PNG, in practice
Choose it for logos, icons, screenshots of text or interfaces, diagrams, and anything that needs a transparent background. Avoid it for photographs unless a system insists; the first measurement above is what a photo costs as PNG. Converting a JPG to PNG does not create transparency either: the image keeps the background it has, and removing it is an editor's job.
JPG, in practice
Choose it for photographs and for anything leaving your control: email, a print shop, a form, an old content system. Keep the quality between 80 and 90 and export each version from the original rather than re-saving a JPG over itself, because every save discards a little more. Two limits: no transparency, and visible artefacts, halos around high-contrast edges, when the quality is pushed too low.
WebP, in practice
Choose it for images on a site you control. It does lossy compression like JPG and lossless with transparency like PNG, and at the same visible quality it is usually the smallest of the three; the third measurement above shows the gap from the other direction. Its limit is acceptance: some upload forms, desktop viewers and older programs still refuse it. For your own pages, use it; for files you hand to other people, fall back to JPG or PNG.
Converting without uploading
The image format converter takes JPG, PNG and WebP and writes any of the three, with a quality slider for JPG and WebP and a fill colour for transparency. It processes the file on your device; the Network tab test in free online tools that do not upload your files shows how to confirm that for yourself. Two notes from the tests: embedded metadata such as a camera's EXIF data is dropped when the image is redrawn, and HEIC photos from an iPhone are not decoded by Chrome, so convert those to JPG on the phone first.
For sizes rather than formats, the social media image sizes guide has the numbers per platform, and a file that must get under a limit goes to compress an image to 100 KB.