Which format to choose
JPG
The safe default. Every device, browser and upload form accepts it, and it produces the smallest files for photographs. It cannot store transparency, so anything see-through gets filled with a solid colour.
PNG
Lossless, so quality settings do not apply. Right for screenshots of text, logos, diagrams, and anything needing a transparent background. Photographs saved as PNG are typically five to ten times larger than the same image as JPG.
WebP
Usually 25 to 35 percent smaller than JPG at matching quality, and it supports transparency. Every current browser reads it, but some older software and a few upload forms still reject it. Ideal for websites, less so for forms.
Converting the wrong way round
Converting a JPG to PNG will not restore quality that was already lost. JPG discards detail permanently when it saves, and PNG simply preserves whatever it is given, usually producing a much larger file containing exactly the same visible information. Convert to PNG when you need transparency or lossless editing from here on, not to repair an image.
Related things people need
Changing format does not always make a file smaller. If you need to hit a specific size limit, the image compressor targets an exact number of kilobytes rather than a format.
For iPhone photos specifically, the dedicated HEIC to JPG page is more direct, and images to PDF will merge a batch into a single document.
What conversion does and does not change
Converting between image formats re-encodes the picture using a different set of rules. What it cannot do is recover information that has already been discarded. A JPG that was heavily compressed contains only what survived that compression, and saving it as PNG preserves exactly those flaws in a much larger file.
This is the most common misunderstanding about format conversion. PNG is described as lossless, which is true, but lossless means it faithfully stores whatever it is given. Give it a degraded image and it faithfully stores the degradation.
The one conversion that genuinely improves things
Converting HEIC to JPG is the exception, and only in a practical sense rather than a technical one. The HEIC file is better in every measurable way — smaller, higher colour depth, more information retained. The conversion makes it worse as an image and vastly more useful as a file, because the whole world can open a JPG.
That trade is worth making when a file is leaving your control, and not worth making for photographs staying on your own devices.
Transparency, and what happens to it
PNG and WebP can store transparency: pixels that are partly or completely see-through, letting whatever sits behind show through. Logos, icons and graphics with rounded corners rely on it.
JPG cannot. When you convert a transparent image to JPG, those pixels must become something, and the standard choice is white — which is why a logo designed for a dark background suddenly appears in an ugly white box. If your image has transparency you need to keep, convert to PNG or WebP rather than JPG, or set the background colour deliberately.
Resizing while converting
Since conversion re-encodes the image anyway, resizing at the same time costs nothing extra and often achieves more than the format change itself. Halving the dimensions of an image quarters the number of pixels, which typically cuts the file by rather more than any format choice would.
If your goal is a smaller file rather than a different format, resizing is usually the more effective lever, and the image compressor combines both while targeting a specific size.
Why some forms reject WebP
WebP is supported by every current browser, which leads people to assume it is universally accepted. Upload forms are a different matter. Many validate file types against a list written years ago, and that list frequently contains only JPG, PNG and sometimes GIF.
The safe rule: use WebP for images you are publishing on a website you control, and JPG for anything being submitted, emailed or shared. The size advantage is real but not worth a rejected application.
Questions
Can I convert iPhone HEIC photos here?
Yes. Drop them in and they are decoded automatically. If you only need HEIC to JPG, the dedicated page is a little more direct.
Are my images uploaded?
No. Conversion happens in your browser, on your device.
Does converting remove location data?
Yes. Re-encoding drops EXIF metadata including GPS coordinates, camera model and timestamp.