Why JPG is still the safe choice
Newer formats are smaller and newer browsers read them, but the systems people actually have to upload to — application portals, older content systems, printers' order pages, office software — often accept only .jpg/.jpeg (and sometimes PNG). When a site says “invalid file type”, converting to JPG is nearly always the fix.
What it converts from
- PNG — including screenshots and images with transparency. See PNG to JPG for when that's a good idea.
- WebP — the format many websites serve images in, which is why “Save image” often gives you a .webp. More on WebP to JPG.
- GIF — the first frame becomes a still JPG.
- BMP — old Windows bitmaps, which are huge; the JPG will be a small fraction of the size.
- JPEG — re-saving at a lower quality makes it smaller. For a precise limit use compress to KB instead.
- HEIC and AVIF — when your browser can open them. Safari on a Mac, iPhone or iPad opens HEIC, the iPhone's default photo format; Chrome and Firefox can't today, and the page will tell you.
Choosing the quality
The slider sets JPEG quality from 40 to 100; it starts at 90, which is visually very close to the original for photos. Lower it for a smaller file: around 75–85 is the usual range for web and email. Above about 95 the file grows quickly with nothing you can see gained. The result shows its size next to the original's so you can try a couple of settings.
What gets lost
- Transparency. JPG has none, so transparent areas become white. Logos and cut-outs that need a transparent background should stay PNG.
- Animation. Only the first frame of an animated GIF is kept.
- Metadata. The new file has no EXIF data — no location, date or camera details. The photo is turned upright first, so it doesn't end up sideways. A colour profile is kept.
JPEG is lossy, so each conversion throws away a little detail you can't get back. Convert from the best original you have, once, rather than converting a converted copy.