Three formats cover almost every everyday image. Instead of repeating the usual advice, we measured what happens to the file when our converter moves pictures between them: on 23 September 2026, 20 photos (3 to 30 megapixels) and 10 screenshots of web pages. Every number below is the new size as a multiple of the old one.
The short answer
- Photos: JPG, or WebP for a website.
- Screenshots, diagrams, text, logos, anything with transparency: PNG — or WebP if it has to be lighter.
- Converting back and forth: only when a program or a form needs a particular format. It never restores quality, and it usually adds size.
Photos
| Conversion | New size vs old (smallest / median / largest) |
|---|---|
| JPG → PNG | ×2.73 / ×3.79 / ×10.02 |
| JPG → WebP (quality 0.92) | ×0.15 / ×0.28 / ×0.76 |
| Photo saved as PNG → JPG | ×0.07 / ×0.11 / ×0.15 |
A photo in PNG is simply large: lossless storage keeps every speck of the sensor's fine noise. Turning such a PNG back into JPG made it about 9 times smaller. WebP at the same 0.92 quality came out at about a quarter of the original JPEG at the median — partly because WebP compresses better, partly because the original files had been saved at a high quality we did not choose.
Screenshots
| Conversion | New size vs old (smallest / median / largest) |
|---|---|
| PNG → JPG | ×1.08 / ×1.23 / ×1.50 |
| PNG → WebP | ×0.49 / ×0.56 / ×0.77 |
For screenshots JPG is the wrong move: every one of the ten got bigger, by 23% at the median, and the sharp edges of letters pick up faint halos. JPEG is designed for smooth photographic detail; large flat areas and crisp text are what PNG stores best. WebP roughly halved the screenshots.
Photos that are already WebP
We also made WebP files the way websites usually carry photos — 1600 pixels on the long side, quality 0.8 — and converted them back.
| Conversion | New size vs old (smallest / median / largest) |
|---|---|
| WebP → JPG | ×1.76 / ×2.35 / ×3.02 |
| WebP → PNG | ×9.50 / ×16.24 / ×23.42 |
Back to JPG costs two to three times the size; to PNG, ten to twenty times. Do it when a program cannot open WebP; otherwise leave the file as it is.
Transparency
PNG and WebP can keep a transparent background; JPG cannot. When our converter writes a JPG, transparent areas are filled with white — which is why a logo on a transparent background should stay PNG or WebP.
Try it
The converter does each of these in the browser, without uploading: PNG to JPG, JPG to PNG, WebP to JPG, WebP to PNG. If what you really need is a smaller file rather than a different format, the compressor is the better tool.