PNG or JPG: when to convert, and what changes
What happens to a PNG when it becomes a JPG, measured on a photo, a screenshot and a transparent logo, and when converting helps or hurts.
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In short
- A photo saved as PNG shrinks a lot as a JPG. Our 3,000 × 4,000 test photo went from 21.20 MB as PNG to 3.63 MB as JPG at 92% quality, and to 1.69 MB at 80%.
- A screenshot gains little. Our 1920 × 1080 screenshot went from 368.0 KB to 305.0 KB, and small text gets slightly softer in a JPG.
- JPG has no transparency. See-through parts of a PNG are filled with a background colour, white unless you choose another.
- The pixel size never changes. For a fixed KB limit, use the Image Resizer in KB after converting.
- Nothing is uploaded. Files are converted in this browser tab.
A form says "upload JPG only", and the photo on your phone or the scan on your laptop is a PNG. Or a PNG photo is 20 MB and will not attach to an email. Converting PNG to JPG fixes both, but it is not free: JPG throws some detail away to save space, and it cannot keep transparency. This guide shows what changes, with measurements from the converter above.
How to convert PNG to JPG
- Choose the PNG files at the top of the page. One file or up to 50 at a time.
- Leave the quality at 92% unless you want smaller files. The background colour only matters if a PNG has transparent areas.
- Download each JPG, or all of them in one ZIP when there are several.
The JPG keeps the PNG's pixel size exactly. A 1920 × 1080 PNG becomes a 1920 × 1080 JPG.
What converting does to the file size
PNG is lossless: it stores every pixel exactly, packed with the same compression as a ZIP file. JPG is lossy: it stores an approximation the eye cannot tell apart from the original, and the approximation is far smaller for the kind of picture JPG was designed for, which is photographs.
We made three test images and put each through the converter at the default 92% quality:
| Test image | Pixels | PNG | JPG | Change |
|---|---|---|---|---|
| Grainy phone-style photo | 3,000 × 4,000 | 21.20 MB | 3.63 MB | about 83% smaller |
| Screenshot with text | 1,920 × 1,080 | 368.0 KB | 305.0 KB | about 17% smaller |
| Logo on a transparent background | 800 × 800 | 35.9 KB | 23.9 KB | about 33% smaller |
The photo is where converting pays. A PNG of a photo carries every grain of sensor noise exactly, which is expensive; a JPG keeps the look of the noise without its exact values. Dropping the quality to 80% took the same photo down to 1.69 MB, less than half the 92% file.
The screenshot barely shrank. Sharp text on flat colour is what PNG compresses well and what JPG handles worst: every letter edge costs JPG bytes, and the plain areas between them cost PNG almost nothing. Real screenshots with large flat areas can even come out bigger as JPG.
Each conversion took between a quarter of a second and 1.5 seconds on a desktop browser.
Quality: what the slider changes
The quality number, 50 to 100 here, tells the JPG encoder how much detail to keep. It is not a percentage of anything you can measure; it is a setting that trades file size against fidelity.
92% is the default because, at normal viewing size, a photo saved at 92 looks the same as the original. Around 80 the file roughly halves again, and only side-by-side comparison at full size shows the difference. Below 70, edges start to show faint blocks and halos, most visibly around text.
For an exact KB limit, do not hunt with the slider. Convert here, then use the Image Resizer in KB or the Resize Image to 50 KB page: they search the quality and, if needed, the pixel size automatically and stop just under the limit.
Transparency and the background colour
A PNG can have transparent pixels: the area around a logo, a signature cut out from paper, a sticker. JPG has no way to store "see-through", so every such pixel needs a real colour.
The converter fills transparent areas with white by default, because a white background is what forms, documents and most printing expect. Our logo test came back with "Transparent parts were filled with the background colour" beside it, which the page shows whenever it finds see-through pixels.
Choose black or any other colour under "Background for transparent areas" when the JPG will sit on a dark page. If you need the transparency itself, keep the PNG: no JPG can carry it.
A semi-transparent edge, such as the soft border of a cut-out signature, is blended with the background colour rather than cut off, so the edge stays smooth.
When to keep the PNG
Converting is the right call when a form or a person asks for JPG, or when a PNG photo is too big to send. Keep the PNG when:
- The picture is a screenshot, a chart or a scanned page of text. JPG softens sharp edges, and the size saving is small.
- It has transparency you need, such as a logo for a website or a sticker.
- You will edit it again. Every time a JPG is opened and saved, a little more detail is lost. Edit the PNG and convert once at the end.
And if the form accepts PNG, there is nothing to gain by converting a small PNG.
Common reasons a converted JPG is rejected
Still too large. Converting does not set a size limit. A 4,000-pixel photo is still several megabytes as a JPG. Use a KB tool after converting.
Wrong pixel size. The converter keeps the size you gave it. If a form wants 200 × 230 pixels, set that on the Image Resizer in KB.
The extension was renamed, not converted. Renaming photo.png to photo.jpg in a file manager does not change what is inside, and a strict portal reads the file's contents. A file made here is a real JPG.
A dark background where white was expected. If the original PNG was transparent and you chose black, the JPG background is black. Convert again with white.
Converting many files at once
Choose up to 50 PNGs in one go: hold Ctrl (Cmd on a Mac) to pick several in the file dialog, or select a whole folder's worth with Ctrl + A. They are converted one after another rather than all together, so a phone does not have to hold fifty full-size pictures in memory at the same moment. Each file shows its own result as soon as it is ready, with its size before and after.
When two or more are done, Download all as ZIP saves every JPG in one file. Each keeps its original name with the new extension, so "Bill March.png" becomes "Bill March.jpg". If two files had the same name, the second becomes "Bill March (2).jpg" inside the ZIP rather than overwriting the first.
Changing the quality or the background colour converts every file again with the new setting. Adding more files later converts only the new ones.
PNG to JPG on a phone
The page works the same in a phone browser. Tap the file button and choose from the gallery or Files; on Android you can choose several pictures at once. The JPGs download to the phone's Downloads folder, where the gallery and every upload form can find them. Nothing has to be installed, and the pictures never leave the phone.
What this tool assumes
- Each image is opened by the browser and saved again as a baseline JPG at the quality chosen, 92% by default, at exactly the same pixel size.
- Transparent and semi-transparent pixels are blended over the background colour, white by default.
- Images up to 50 megapixels are converted; larger ones are refused, because a canvas that size can run a phone out of memory.
- Up to 50 files are taken at once and converted one after another. Several JPGs can be saved together as a ZIP.
- The files stay on your device. The new JPGs carry none of the camera or location details stored in the originals.