Which image format should you use
WebP is the default choice for the web now. It produces noticeably smaller files than JPG at the same visual quality and supports transparency like PNG. Every current browser handles it. The only time to avoid it is when something downstream — an older CMS, a print workflow, a marketplace upload form — refuses to accept it.
JPG is the safe option. It is understood by everything, and for photographs it is still perfectly good. It cannot do transparency, and every save loses a little more detail, so avoid repeatedly re-saving the same JPG.
PNG is lossless, which makes it right for logos, screenshots, diagrams and anything with sharp edges or flat colour. That also makes it heavy for photographs — a photo saved as PNG is often five to ten times larger than the same image as WebP.
One thing worth knowing: converting to PNG from a JPG does not restore quality that was already lost. It just stops any further loss from that point on.
Which format should you convert to?
WebP is the default answer for anything going on a website. It produces noticeably smaller files than JPG at the same visual quality and supports transparency like PNG. Every current browser handles it. The only reason to avoid it is a downstream system that refuses to accept it — an older CMS, a print workflow, a marketplace upload form.
JPG is the safe option: understood by everything, and still perfectly good for photographs. It cannot do transparency, and every save discards a little more detail.
PNG is lossless, which makes it right for logos, screenshots, diagrams and anything with sharp edges or flat colour. That also makes it heavy for photographs — a photo saved as PNG is often five to ten times the size of the same image as WebP.
Converting to PNG does not restore quality
This one costs people time. If an image has already been saved as JPG, detail has already been discarded, and converting it to PNG cannot bring it back. What PNG does is stop further loss from that point on.
The practical rule: keep an original in a lossless format if you can, and export copies. Repeatedly opening and re-saving the same JPG degrades it a little each time, which is why images passed around a team eventually look soft.
Resize before you convert, not after
A 4000-pixel-wide photo displayed in a 800-pixel column is sending four times the data for no visible benefit, whatever format it is in. Resizing is almost always the bigger saving — often 80% or more against the 20–40% a format change buys you.
Set a max dimension that matches the widest place the image will actually appear. For most blog content 1200–1600 pixels is plenty; for a thumbnail, far less. This tool does both in one pass, so you are not exporting twice.
Why conversion here happens on your device
Every conversion runs in your browser through the canvas API. The file is read locally, redrawn and re-encoded locally, and the result is handed straight back to you. Nothing is uploaded, which means no queue, no file-size ceiling imposed by a server, and nothing of yours sitting on someone else’s disk.
You can verify this yourself: open your browser’s network tab, convert an image, and watch that no request is made.
Batch conversion and file names
Up to twenty images can be converted at once, and each keeps its original name with a new extension. That matters more than it sounds: if you are replacing images on a site, matching names means you can swap files without editing every reference.
If you need an exact file size rather than a format change — an upload form demanding under 200 KB, say — the compress to an exact KB size tool targets a number instead.