Take one photo of a sunset and save it two ways. As a PNG it's 4.2 MB. As a JPG at quality 85, it's about 460 KB — and side by side, you can't tell them apart. Now screenshot a spreadsheet. As a PNG it's 88 KB with razor-sharp text. Save that same screenshot as a JPG and it balloons to ~150 KB and the numbers grow fuzzy grey halos. Same two source images, opposite winners. That flip is the entire PNG-vs-JPG decision in one experiment.
Most people pick a format out of habit — whatever their screenshot tool spits out, or whatever the "Save As" box happens to default to. But the two formats are built for opposite jobs, and using the wrong one either bloats your file or wrecks the image.
What the two formats actually do
JPG (also written JPEG) uses lossy compression. It throws away image data your eye is unlikely to notice, then compresses what's left. That's why it's so small, and why every save degrades the image a little. It also has no transparency: a JPG is always a solid rectangle of pixels.
PNG uses lossless compression. It shrinks the file without discarding a single pixel of information. Decode it and you get back the exact original. It also supports an alpha channel, meaning parts of the image can be fully or partly transparent. That's the format behind logos that sit cleanly on any background.
The short version: JPG trades quality for size. PNG keeps quality and transparency but pays for it in bytes.
When JPG is the right call
JPG was designed for photographs, and it's still excellent at them. Photos are full of gradients and subtle color shifts (grass, skin, sky) where the data JPG discards genuinely doesn't matter to your eye.
The numbers make the case. A 12-megapixel phone photo saved as a lossless PNG can run 8–15 MB. The same photo as JPG at quality 80–90 lands around 2–4 MB with no visible loss. On a website, that's the difference between a page that loads instantly and one that stalls.
Use JPG for: photographs, realistic images, anything with lots of continuous color and no hard edges — email attachments, product photos, blog header images, social uploads.
When PNG is the right call
The moment an image has sharp edges, text, flat color blocks, or transparency, PNG wins — often on both quality and size.
Screenshots are the clearest example. A screenshot is mostly flat backgrounds and crisp text, which is exactly what PNG compresses efficiently and JPG handles badly. JPG's compression smears the boundary between black text and a white background, leaving the grey fringing ("ringing artifacts") you've seen on re-saved memes. PNG keeps every edge pixel-perfect.
Use PNG for: logos and icons, screenshots, diagrams and charts, line art, images with text, and anything that needs a transparent background. A logo saved as JPG comes back with a white box around it and fuzzy edges — a dead giveaway of the wrong format.
What actually happens when you convert PNG to JPG
Converting is often a reasonable move — a photo mistakenly saved as a giant PNG is a perfect candidate to shrink. But know the two things you give up.
Transparency disappears. JPG has no alpha channel, so every transparent pixel gets filled with a solid color — usually white, sometimes black. A logo with a see-through background becomes a logo stuck on a white rectangle. There's no undo once it's flattened.
It's a permanent re-compression. The moment you save as JPG, the lossy step runs and detail is gone for good. Converting back to PNG afterward doesn't recover it — you just wrap the already-degraded image in a lossless container. And each additional JPG re-save degrades it further (generation loss), which is why forwarded images slowly turn to mush.
A browser tool like PNG to JPG handles the conversion in a couple of clicks — and because it runs entirely in your browser, your image never gets uploaded to a server. For a screenshot or a personal photo, that privacy is worth more than most people think.
When neither PNG nor JPG is the answer (honest limits)
Two honest caveats.
First, converting PNG to JPG only saves space when the image is photographic. Run a screenshot or a flat-color graphic through the conversion and you can end up with a file that's both larger and uglier than the PNG you started with. Check the output size before you commit; don't assume JPG is always smaller.
Second, PNG and JPG aren't the only options, and often not the best ones. WebP typically beats both — it does lossy and lossless, supports transparency, and lands 25–35% smaller than JPG at the same quality. AVIF goes smaller still. Every current browser supports WebP, so for a website you control, it's usually the smarter choice. Where PNG and JPG win is universal compatibility: they open everywhere, on everything, with zero surprises. For emailing a client, printing at a shop, or uploading to a platform with picky requirements, that reliability beats a few saved kilobytes.
And if your real problem is a JPG photo that's simply too big, converting formats won't help — you want to compress or resize it, not change what it is.
The rule that covers 95% of cases
Ask one question: does the image have sharp edges, text, or transparency?
- Yes → PNG. Screenshots, logos, icons, diagrams, anything with a transparent background.
- No, it's a photo → JPG at quality 80–90. You'll cut the file to a fraction of the PNG size with no visible loss.
That single question resolves nearly every case correctly. Then keep the original of anything important: if you have the source PNG, you can always make a JPG later, but a JPG can never give you back the pixels it threw away. Convert down when you need the smaller file — and hoard the lossless original.